integration host factor

組込み宿主因子

WordNet

1. be the host of or for; "We hosted 4 couples last night"
2. an animal or plant that nourishes and supports a parasite; it does not benefit and is often harmed by the association
3. the owner or manager of an inn (同)innkeeper, boniface
4. archaic terms for army (同)legion
5. (medicine) recipient of transplanted tissue or organ from a donor
6. a person who invites guests to a social event (such as a party in his or her own home) and who is responsible for them while they are there
7. any organization that provides resources and facilities for a function or event; "Atlanta was chosen to be host for the Olympic Games"
8. be a contributing factor; "make things factor into a companys profitability"
9. any of the numbers (or symbols) that form a product when multiplied together
10. an independent variable in statistics
11. anything that contributes causally to a result; "a number of factors determined the outcome"
12. consider as relevant when making a decision; "You must factor in the recent developments" (同)factor in, factor out
13. resolve into factors; "a quantum computer can factor the number 15" (同)factor in, factor out
14. an event known to have happened or something known to have existed; "your fears have no basis in fact"; "how much of the story is fact and how much fiction is hard to tell"
15. a concept whose truth can be proved; "scientific hypotheses are not facts"
16. a piece of information about circumstances that exist or events that have occurred; "first you must collect all the facts of the case"
17. a statement or assertion of verified information about something that is the case or has happened; "he supported his argument with an impressive array of facts"
18. the action of incorporating a racial or religious group into a community (同)integrating, desegregation
19. an operation used in the calculus whereby the integral of a function is determined

PrepTutorEJDIC

1. (…の)大群,大勢《+『of』+『名』》(multitude)
2. (客を接待する)『主人』,『主人役』;(…の)主人[役]《+『to』+『名』》 / (旅館の)主人 / 寄生動(植)物の宿主 / 〈晩餐会など〉‘の'主人役を務める,‘を'主催する
3. (…の)『要因』,(…を生み出す)要素《+『in』+『名』(do『ing』)》 / 囲数,約数 / 代理人,《おもに英》仲買人 / =factorize
4. 〈C〉『事実』,実際にある(あった)事 / 〈U〉真相,真実(truth) / 《the~》(法律用語で)犯行
5. 統合,集成,完成 / (学校や住居における)人種差別の撤廃
6. ほう(驚き・賞賛・冷笑などの発声);お‐い(呼びかけ・注意などの発声)
7. 娼婦・売春婦：（whoreの発音をくずしたもの）

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2019/09/03 05:07:04」(JST)

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Enterobacteria phage λ
Lysis plaques of lambda phage on E. coli bacteria
Virus classification
Group:	Group I (dsDNA)
Order:	Caudovirales
Family:	Siphoviridae
Genus:	Lambdavirus
Species:	λ phage

Enterobacteria phage λ (lambda phage, coliphage λ, officially Escherichia virus Lambda) is a bacterial virus, or bacteriophage, that infects the bacterial species Escherichia coli (E. coli). It was discovered by Esther Lederberg in 1950. The wild type of this virus has a temperate lifecycle that allows it to either reside within the genome of its host through lysogeny or enter into a lytic phase (during which it kills and lyses the cell to produce offspring); mutant strains are unable to lysogenize cells – instead, they grow and enter the lytic cycle after superinfecting an already lysogenized cell.

The phage particle consists of a head (also known as a capsid), a tail, and tail fibers (see image of virus below). The head contains the phage's double-strand linear DNA genome. During infection, the phage particle recognizes and binds to its host, E. coli, causing DNA in the head of the phage to be ejected through the tail into the cytoplasm of the bacterial cell. Usually, a "lytic cycle" ensues, where the lambda DNA is replicated and new phage particles are produced within the cell. This is followed by cell lysis, releasing the cell contents, including virions that have been assembled, into the environment. However, under certain conditions, the phage DNA may integrate itself into the host cell chromosome in the lysogenic pathway. In this state, the λ DNA is called a prophage and stays resident within the host's genome without apparent harm to the host. The host is termed a lysogen when a prophage is present. This prophage may enter the lytic cycle when the lysogen enters a stressed condition.

Anatomy

Bacteriophage lambda virion (schematic). Protein names and their copy numbers in the virion particle are shown. The presence of the L and M proteins in the virion is still unclear.

The virus particle consists of a head and a tail that can have tail fibers. The whole particle consists of 12–14 different proteins with more than 1000 protein molecules total and one DNA molecule located in the phage head. However, it is still not entirely clear whether the L and M proteins are part of the virion.

Linear layout of lambda phage genome with major operons, promoter regions and capsid coding genes.

The genome contains 48,490 base pairs of double-stranded, linear DNA, with 12-base single-strand segments at both 5' ends. These two single-stranded segments are the "sticky ends" of what is called the cos site. The cos site circularizes the DNA in the host cytoplasm. In its circular form, the phage genome, therefore, is 48,502 base pairs in length. The lambda genome can be inserted into the E. coli chromosome and is then called a prophage. See section below for details.

Life cycle

Infection

Lambda phage J protein interaction with the LamB porin

Lambda phage is a non-contractile tailed phage, meaning during an infection event it cannot 'force' its DNA through a bacterial cell membrane. It must instead use an existing pathway to invade the host cell, having evolved the tip of its tail to interact with a specific pore to allow entry of its DNA to the hosts.

1. Bacteriophage Lambda binds to an E. coli cell by means of its J protein in the tail tip. The J protein interacts with the maltose outer membrane porin (the product of the lamB gene) of E. coli, a porin molecule, which is part of the maltose operon.
2. The linear phage genome is injected through the outer membrane.

1. The DNA passes through the mannose permease complex in the inner membrane (encoded by the manXYZ genes) and immediately circularises using the cos sites, 12-base G-C-rich cohesive "sticky ends". The single-strand viral DNA ends are ligated by host DNA ligase.

Lambda phage DNA injection into the cell membrane using Mannose PTS permease a sugar transporting system as a mechanism of entry into the cytoplasm.

1. Host DNA gyrase puts negative supercoils in the circular chromosome, causing A-T-rich regions to unwind and drive transcription.
2. Transcription starts from the constitutive P_L, P_R and P_R' promoters producing the 'immediate early' transcripts. At first, these express the N and cro genes, producing N, Cro and a short inactive protein.

Early activation events involving N protein

1. Cro binds to OR3, preventing access to the P_RM promoter, preventing expression of the cI gene. N binds to the two Nut (N utilisation) sites, one in the N gene in the P_L reading frame, and one in the cro gene in the P_R reading frame.
2. The N protein is an antiterminator, and functions to extend the reading frames to which it is bound. When RNA polymerase transcribes these regions, it recruits the N and forms a complex with several host Nus proteins. This complex skips through most termination sequences. The extended transcripts (the 'late early' transcripts) include the N and cro genes along with cII and cIII genes, and xis, int, O, P and Q genes discussed later.
3. The cIII protein acts to protect the cII protein from proteolysis by FtsH (a membrane-bound essential E. coli protease) by acting as a competitive inhibitor. This inhibition can induce a bacteriostatic state, which favours lysogeny. cIII also directly stabilises the cII protein.

On initial infection, the stability of cII determines the lifestyle of the phage; stable cII will lead to the lysogenic pathway, whereas if cII is degraded the phage will go into the lytic pathway. Low temperature, starvation of the cells and high multiplicity of infection (MOI) are known to favor lysogeny (see later discussion).

N antitermination

N Antitermination requires the assembly of a large ribonucleoprotein complex to effectively prolong the anti-termination process, without the full complex the RNA polymerase is able to bypass only a single terminator

This occurs without the N protein interacting with the DNA; the protein instead binds to the freshly transcribed mRNA. Nut sites contain 3 conserved "boxes," of which only BoxB is essential.

1. The boxB RNA sequences are located close to the 5' end of the pL and pR transcripts. When transcribed, each sequence forms a hairpin loop structure that the N protein can bind to.
2. N protein binds to boxB in each transcript, and contacts the transcribing RNA polymerase via RNA looping. The N-RNAP complex is stabilized by subsequent binding of several host Nus (N utilisation substance) proteins (which include transcription termination/antitermination factors and, bizarrely, a ribosome subunit).
3. The entire complex (including the bound Nut site on the mRNA) continues transcription, and can skip through termination sequences.

Lytic life cycle

Main article: Lytic cycle

This is the lifecycle that the phage follows following most infections, where the cII protein does not reach a high enough concentration due to degradation, so does not activate its promoters.

1. The 'late early' transcripts continue being written, including xis, int, Q and genes for replication of the lambda genome (OP). Cro dominates the repressor site (see "Repressor" section), repressing synthesis from the P_RM promoter (which is a promoter of the lysogenic cycle).
2. The O and P proteins initiate replication of the phage chromosome (see "Lytic Replication").
3. Q, another antiterminator, binds to Qut sites.
4. Transcription from the P_R' promoter can now extend to produce mRNA for the lysis and the head and tail proteins.
5. Structural proteins and phage genomes self-assemble into new phage particles.
6. Products of the lysis genes S,R, Rz and Rz1 cause cell lysis. S is a holin, a small membrane protein that, at a time determined by the sequence of the protein, suddenly makes holes in the membrane. R is an endolysin, an enzyme that escapes through the S holes and cleaves the cell wall. Rz and Rz1 are membrane proteins that form a complex that somehow destroys the outer membrane, after the endolysin has degraded the cell wall. For wild-type lambda, lysis occurs at about 50 minutes after the start of infection and releases around 100 virions.

Rightward transcription

Rightward transcription expresses the O, P and Q genes. O and P are responsible for initiating replication, and Q is another antiterminator that allows the expression of head, tail, and lysis genes from P_R’.

Lytic replication

1. For the first few replication cycles, the lambda genome undergoes θ replication (circle-to-circle).
2. This is initiated at the ori site located in the O gene. O protein binds the ori site, and P protein binds the DnaB subunit of the host replication machinery as well as binding O. This effectively commandeers the host DNA polymerase.
3. Soon, the phage switches to a rolling circle replication similar to that used by phage M13. The DNA is nicked and the 3’ end serves as a primer. Note that this does not release single copies of the phage genome but rather one long molecule with many copies of the genome: a concatemer.
4. These concatemers are cleaved at their cos sites as they are packaged. Packaging cannot occur from circular phage DNA, only from concatomeric DNA.

Q antitermination

The Q protein modifies the RNA polymerase at the promoter region and is recruited to RNA polymerase. The Q protein turns into a RNA polymerase subunit after it is recruitment to RNAP and modifies the enzyme into a processive state. Note that NusA can stimulate the activity of the Q protein.

Q is similar to N in its effect: Q binds to RNA polymerase in Qut sites and the resulting complex can ignore terminators, however the mechanism is very different; the Q protein first associates with a DNA sequence rather than an mRNA sequence.

1. The Qut site is very close to the P_R’ promoter, close enough that the σ factor has not been released from the RNA polymerase holoenzyme. Part of the Qut site resembles the -10 Pribnow box, causing the holoenzyme to pause.
2. Q protein then binds and displaces part of the σ factor and transcription re-initiates.
3. The head and tail genes are transcribed and the corresponding proteins self-assemble.

Leftward transcription

Diagram showing the retro-regulation process that yields a higher concentration of xis compared to int. The mRNA transcript is digested by bacterial RNase starting from the cleaved hairpin loop at sib.

Leftward transcription expresses the gam, red, xis, and int genes. Gam and red proteins are involved in recombination. Gam is also important in that it inhibits the host RecBCD nuclease from degrading the 3’ ends in rolling circle replication. Int and xis are integration and excision proteins vital to lysogeny.

xis and int regulation of insertion and excision

1. xis and int are found on the same piece of mRNA, so approximately equal concentrations of xis and int proteins are produced. This results (initially) in the excision of any inserted genomes from the host genome.
2. The mRNA from the P_L promoter forms a stable secondary structure with a stem-loop in the sib section of the mRNA. This targets the 3' (sib) end of the mRNA for RNAaseIII degradation, which results in a lower effective concentration of int mRNA than xis mRNA (as the int cistron is nearer to the sib sequence than the xis cistron is to the sib sequence), so a higher concentrations of xis than int is observed.
3. Higher concentrations of xis than int result in no insertion or excision of phage genomes, the evolutionarily favoured action - leaving any pre-insterted phage genomes inserted (so reducing competition) and preventing the insertion of the phage genome into the genome of a doomed host.

Lysogenic (or lysenogenic) life cycle

Main article: Lysogenic cycle

The lysogenic lifecycle begins once the cI protein reaches a high enough concentration to activate its promoters, after a small number of infections.

1. The 'late early' transcripts continue being written, including xis, int, Q and genes for replication of the lambda genome.
2. The stabilized cII acts to promote transcription from the P_RE, P_I and P_antiq promoters.
3. The P_antiq promoter produces antisense mRNA to the Q gene message of the P_R promoter transcript, thereby switching off Q production. The P_RE promoter produces antisense mRNA to the cro section of the P_R promoter transcript, turning down cro production, and has a transcript of the cI gene. This is expressed, turning on cI repressor production. The P_I promoter expresses the int gene, resulting in high concentrations of Int protein. This int protein integrates the phage DNA into the host chromosome (see "Prophage Integration").
4. No Q results in no extension of the P_R' promoter's reading frame, so no lytic or structural proteins are made. Elevated levels of int (much higher than that of xis) result in the insertion of the lambda genome into the hosts genome (see diagram). Production of cI leads to the binding of cI to the OR1 and OR2 sites in the P_R promoter, turning off cro and other early gene expression. cI also binds to the P_L promoter, turning off transcription there too.
5. Lack of cro leaves the OR3 site unbound, so transcription from the P_RM promoter may occur, maintaining levels of cI.
6. Lack of transcription from the P_L and P_R promoters leads to no further production of cII and cIII.
7. As cII and cIII concentrations decrease, transcription from the P_antiq, P_RE and P_I stop being promoted since they are no longer needed.
8. Only the P_RM and P_R' promoters are left active, the former producing cI protein and the latter a short inactive transcript. The genome remains inserted into the host genome in a dormant state.

The prophage is duplicated with every subsequent cell division of the host. The phage genes expressed in this dormant state code for proteins that repress expression of other phage genes (such as the structural and lysis genes) in order to prevent entry into the lytic cycle. These repressive proteins are broken down when the host cell is under stress, resulting in the expression of the repressed phage genes. Stress can be from starvation, poisons (like antibiotics), or other factors that can damage or destroy the host. In response to stress, the activated prophage is excised from the DNA of the host cell by one of the newly expressed gene products and enters its lytic pathway.

Prophage integration

The integration of phage λ takes place at a special attachment site in the bacterial and phage genomes, called att^λ. The sequence of the bacterial att site is called attB, between the gal and bio operons, and consists of the parts B-O-B', whereas the complementary sequence in the circular phage genome is called attP and consists of the parts P-O-P'. The integration itself is a sequential exchange (see genetic recombination) via a Holliday junction and requires both the phage protein Int and the bacterial protein IHF (integration host factor). Both Int and IHF bind to attP and form an intasome, a DNA-protein-complex designed for site-specific recombination of the phage and host DNA. The original B-O-B' sequence is changed by the integration to B-O-P'-phage DNA-P-O-B'. The phage DNA is now part of the host's genome.

Maintenance of lysogeny

A simplified representation of the integration/excision paradigm and the major genes involved.

• Lysogeny is maintained solely by cI. cI represses transcription from P_L and P_R while upregulating and controlling its own expression from P_RM. It is therefore the only protein expressed by lysogenic phage.

Lysogen repressors and polymerase bound to OR1 and recruits OR2, which will activate PRM and shutdown PR.

• This is coordinated by the P_L and P_R operators. Both operators have three binding sites for cI: OL1, OL2, and OL3 for P_L, and OR1, OR2 and OR3 for P_R.
• cI binds most favorably to OR1; binding here inhibits transcription from P_R. As cI easily dimerises, the binding of cI to OR1 greatly increases the affinity of the binding of cI to OR2, and this happens almost immediately after OR1 binding. This activates transcription in the other direction from P_RM, as the N terminal domain of cI on OR2 tightens the binding of RNA polymerase to P_RM and hence cI stimulates its own transcription. When it is present at a much higher concentration, it also binds to OR3, inhibiting transcription from P_RM, thus regulating its own levels in a negative feedback loop.
• cI binding to the P_L operator is very similar, except that it has no direct effect on cI transcription. As an additional repression of its own expression, however, cI dimers bound to OR3 and OL3 bend the DNA between them to tetramerise.
• The presence of cI causes immunity to superinfection by other lambda phages, as it will inhibit their P_L and P_R promoters.

Induction

Transcriptional state of the P_RM and P_R promoter regions during a lysogenic state vs induced, early lytic state.

The classic induction of a lysogen involved irradiating the infected cells with UV light. Any situation where a lysogen undergoes DNA damage or the SOS response of the host is otherwise stimulated leads to induction.

1. The host cell, containing a dormant phage genome, experiences DNA damage due to a high stress environment, and starts to undergo the SOS response.
2. RecA (a cellular protein) detects DNA damage and becomes activated. It is now RecA*, a highly specific co-protease.
3. Normally RecA* binds LexA (a transcription repressor), activating LexA auto-protease activity, which destroys LexA repressor, allowing production of DNA repair proteins. In lysogenic cells, this response is hijacked, and RecA* stimulates cI autocleavage. This is because cI mimics the structure of LexA at the autocleavage site.
4. Cleaved cI can no longer dimerise, and loses its affinity for DNA binding.
5. The P_R and P_L promoters are no longer repressed and switch on, and the cell returns to the lytic sequence of expression events (note that cII is not stable in cells undergoing the SOS response). There is however one notable difference.

The function of LexA in the SOS response. LexA expression leads to inhibition of various genes including LexA.

Control of phage genome excision in induction

1. The phage genome is still inserted in the host genome and needs excision for DNA replication to occur. The sib section beyond the normal P_L promoter transcript is, however, no longer included in this reading frame (see diagram).
2. No sib domain on the P_L promoter mRNA results in no hairpin loop on the 3' end, and the transcript is no longer targeted for RNAaseIII degradation.
3. The new intact transcript has one copy of both xis and int, so approximately equal concentrations of xis and int proteins are produced.
4. Equal concentrations of xis and int result in the excision of the inserted genome from the host genome for replication and later phage production.

Multiplicity reactivation and prophage reactivation

Multiplicity reactivation (MR) is the process by which multiple viral genomes, each containing inactivating genome damage, interact within an infected cell to form a viable viral genome. MR was originally discovered with phage T4, but was subsequently found in phage λ (as well as in numerous other bacterial and mammalian viruses). MR of phage λ inactivated by UV light depends on the recombination function of either the host or of the infecting phage. Absence of both recombination systems leads to a loss of MR.

Survival of UV-irradiated phage λ is increased when the E. coli host is lysogenic for an homologous prophage, a phenomenon termed prophage reactivation. Prophage reactivation in phage λ appears to occur by a recombinational repair process similar to that of MR.

Repressor

Protein interactions that lead to either Lytic or Lysogenic cycles for Lambda phage

The repressor found in the phage lambda is a notable example of the level of control possible over gene expression by a very simple system. It forms a 'binary switch' with two genes under mutually exclusive expression, as discovered by Barbara J. Meyer.

Visual representation of repressor tetramer/octamer binding to phage lambda L and R operator sites (stable lysogenic state)

The lambda repressor gene system consists of (from left to right on the chromosome):

• cI gene
• O_R3
• O_R2
• O_R1
• cro gene

The lambda repressor is a self assembling dimer also known as the cI protein. It binds DNA in the helix-turn-helix binding motif. It regulates the transcription of the cI protein and the Cro protein.

The life cycle of lambda phages is controlled by cI and Cro proteins. The lambda phage will remain in the lysogenic state if cI proteins predominate, but will be transformed into the lytic cycle if cro proteins predominate.

The cI dimer may bind to any of three operators, O_R1, O_R2, and O_R3, in the order O_R1 = O_R2 > O_R3.

Binding of a cI dimer to O_R1 enhances binding of a second cI dimer to O_R2, an effect called cooperativity. Thus, O_R1 and O_R2 are almost always simultaneously occupied by cI. However, this does not increase the affinity between cI and O_R3, which will be occupied only when the cI concentration is high.

At high concentrations of cI, the dimers will also bind to operators O_L1 and O_L2 (which are over 2 kb downstream from the R operators). When cI dimers are bound to O_L1, O_L2, O_R1, and O_R2 a loop is induced in the DNA, allowing these dimers to bind together to form an octamer. This is a phenomenon called long-range cooperativity. Upon formation of the octamer, cI dimers may cooperatively bind to O_L3 and O_R3, repressing transcription of cI. This autonegative regulation ensures a stable minimum concentration of the repressor molecule and, should SOS signals arise, allows for more efficient prophage induction.

• In the absence of cI proteins, the cro gene may be transcribed.
• In the presence of cI proteins, only the cI gene may be transcribed.
• At high concentration of cI, transcriptions of both genes are repressed.

• Some base pairs with serve a dual function with promoter and operator for either cl and cro proteins.

• Protein cl turned ON, with repressor bound to OR2 polymerase binding is increased and turn OFF OR1.

• Lysogen repression all 3 sites bound is a low occurrence due to OR3 weak binding affinity. OR1 repression increases binding affinity to OR2 due to repressor-repressor interaction. Increased concentrations of repressor increase binding.

Protein function overview

Protein	Function in life cycle	Promoter region	Description
cIII	Regulatory protein CIII. Lysogeny, cII Stability	PL	(Clear 3) HflB (FtsH) binding protein, protects cII from degradation by proteases.
cII	Lysogeny, Transcription activator	PR	(Clear 2) Activates transcription from the PAQ, PRE and PI promoters, transcribing cI and int. Low stability due to susceptibility to cellular HflB (FtsH) proteases (especially in healthy cells and cells undergoing the SOS response). High levels of cII will push the phage toward integration and lysogeny while low levels of cII will result in lysis.
cI	Repressor, Maintenance of Lysogeny	PRM, PRE	(Clear 1) Transcription inhibitor, binds OR1, OR2 and OR3 (affinity OR1 > OR2 = OR3, i.e. preferentially binds OR1). At low concentrations blocks the PR promoter (preventing cro production). At high concentrations downregulates its own production through OR3 binding. Repressor also inhibits transcription from the PL promoter. Susceptible to cleavage by RecA* in cells undergoing the SOS response.
cro	Lysis, Control of Repressor's Operator	PR	Transcription inhibitor, binds OR3, OR2 and OR1 (affinity OR3 > OR2 = OR1, i.e. preferentially binds OR3). At low concentrations blocks the pRM promoter (preventing cI production). At high concentrations downregulates its own production through OR2 and OR1 binding. No cooperative binding (c.f. below for cI binding)
O	Lysis, DNA replication	PR	Replication protein O. Initiates Phage Lambda DNA replication by binding at ori site.
P	Lysis, DNA Replication	PR	Initiates Phage Lambda DNA replication by binding to O and DnaB subunit. These bindings provide control over the host DNA polymerase.
gam	Lysis, DNA replication	PL	Inhibits host RecBCD nuclease from degrading 3' ends—allow rolling circle replication to proceed.
S	Lysis	PR'	Holin, a membrane protein that perforates the membrane during lysis.
R	Lysis	PR'	Endolysin, Lysozyme, an enzyme that exits the cell through the holes produced by Holin and cleaves apart the cell wall.
Rz and Rz1	Lysis	PR'	Forms a membrane protein complex that destroys the outer cell membrane following the cell wall degradation by endolysin. Spanin, Rz1(outer membrane subunit) and Rz(inner membrane subunit).
F	Lysis	PR'	Phage capsid head proteins.
D	Lysis	PR'	Head decoration protein.
E	Lysis	PR'	Major head protein.
C	Lysis	PR'	Minor capsid protein.
B	Lysis	PR'	Portal protein B.
A	Lysis	PR'	Large terminase protein.
J	Lysis	PR'	Host specificity protein J.
M V U G L T Z	Lysis	PR'	Minor tail protein M.
K	Lysis	PR'	Probable endopeptidase.
H	Lysis	PR'	Tail tape measure protein H.
I	Lysis	PR'	Tail assembly protein I.
FI	Lysis	PR'	DNA-packing protein FI.
FII	Lysis	PR'	Tail attachment protein.
tfa	Lysis	PR'	Tail fiber assembly protein.
int	Genome Integration, Excision	PI, PL	Integrase, manages insertion of phage genome into the host's genome. In Conditions of low int concentration there is no effect. If xis is low in concentration and int high then this leads to the insertion of the phage genome. If xis and int have high (and approximately equal) concentrations this leads to the excision of phage genomes from the host's genome.
xis	Genome Excision	PI, PL	Excisionase and int protein regulator, manages excision and insertion of phage genome into the host's genome.
N	Antitermination for Transcription of Late Early Genes	PL	Antiterminator, RNA-binding protein and RNA polymerase cofactor, binds RNA (at Nut sites) and transfers onto the nascent RNApol that just transcribed the nut site. This RNApol modification prevents its recognition of termination sites, so normal RNA polymerase termination signals are ignored and RNA synthesis continues into distal phage genes (cII, cIII, xis, int, O, P, Q)
Q	Antitermination for Transcription of Late Lytic Genes	PR	Antiterminator, DNA binding protein and RNApol cofactor, binds DNA (at Qut sites) and transfers onto the initiating RNApol. This RNApol modification alters its recognition of termination sequences, so normal ones are ignored; special Q termination sequences some 20,000 bp away are effective. Q-extended transcripts include phage structural proteins (A-F, Z-J) and lysis genes (S, R, Rz and Rz1). Downregulated by Pantiq antisense mRNA during lysogeny.
RecA	SOS Response	Host protein	DNA repair protein, functions as a co-protease during SOS response, auto-cleaving LexA and cI and facilitating lysis.

Lytic vs. Lysogenic

Diagram of temperate phage life cycle, showing both lytic and lysogenic cycles.

An important distinction here is that between the two decisions; lysogeny and lysis on infection, and continuing lysogeny or lysis from a prophage. The latter is determined solely by the activation of RecA in the SOS response of the cell, as detailed in the section on induction. The former will also be affected by this; a cell undergoing an SOS response will always be lysed, as no cI protein will be allowed to build up. However, the initial lytic/lysogenic decision on infection is also dependent on the cII and cIII proteins.

In cells with sufficient nutrients, protease activity is high, which breaks down cII. This leads to the lytic lifestyle. In cells with limited nutrients, protease activity is low, making cII stable. This leads to the lysogenic lifestyle. cIII appears to stabilize cII, both directly and by acting as a competitive inhibitor to the relevant proteases. This means that a cell "in trouble", i.e. lacking in nutrients and in a more dormant state, is more likely to lysogenise. This would be selected for because the phage can now lie dormant in the bacterium until it falls on better times, and so the phage can create more copies of itself with the additional resources available and with the more likely proximity of further infectable cells.

A full biophysical model for lambda's lysis-lysogeny decision remains to be developed. Computer modeling and simulation suggest that random processes during infection drive the selection of lysis or lysogeny within individual cells. However, recent experiments suggest that physical differences among cells, that exist prior to infection, predetermine whether a cell will lyse or become a lysogen.

Lambda as a genetic tool

Lambda phage has been used heavily as a model organism, and has been a rich source for useful tools in microbial genetics, and later in molecular genetics. Uses include its application as a vector for the cloning of recombinant DNA; the use of its site-specific recombinase (int) for the shuffling of cloned DNAs by the gateway method; and the application of its Red operon, including the proteins Red alpha (also called 'exo'), beta and gamma in the DNA engineering method called recombineering. The 48 kb DNA fragment of lambda phage is not essential for productive infection and can be replaced by foreign DNA. Lambda phage will enter bacteria more easily than plasmids making it a useful vector that can destroy or can become part of the host's DNA. Lambda phage can be manipulated and used as an anti-cancer vaccine, nanoparticle, targeting human aspartyl (asparaginyl) β-hydroxylase (HAAH). Lambda phage has also been of major importance in the study of specialized transduction.

See also

• Lambda holin family
• Molecular weight size marker
• Zygotic induction
• Esther Lederberg
• Sankar Adhya

Further reading

• James Watson, Tania Baker, Stephen Bell, Alexander Gann, Michael Levine, Richard Losick " Molecular Biology of the Gene (International Edition)" - 6th Edition
• Mark Ptashne and Nancy Hopkins, "The Operators Controlled by the Lambda Phage Repressor", PNAS, v.60, n.4, pp. 1282–1287 (1968).
• Barbara J. Meyer, Dennis G. Kleid, and Mark Ptashne, "Lambda Repressor Turns Off Transcription of Its Own Gene", PNAS, v.72, n.12, pp. 4785–4789 (December 1975).
• Brüssow H, Hendrix RW (January 2002). "Phage genomics: small is beautiful". Cell. 108 (1): 13–6. doi:10.1016/S0092-8674(01)00637-7. PMID 11792317.
• Dodd IB, Shearwin KE, Egan JB (April 2005). "Revisited gene regulation in bacteriophage lambda". Current Opinion in Genetics & Development. 15 (2): 145–52. doi:10.1016/j.gde.2005.02.001. PMID 15797197.
• Friedman DI, Court DL (April 2001). "Bacteriophage lambda: alive and well and still doing its thing". Current Opinion in Microbiology. 4 (2): 201–7. doi:10.1016/S1369-5274(00)00189-2. PMID 11282477.
• Gottesman, M. and Weisberg, R.A. 2004 "Little lambda - who made thee?", Micro and Mol Biol Revs, 68, 796-813 (available online at Microbiology and Molecular Biology Reviews, American Society for Microbiology)
• Hendrix RW, Smith MC, Burns RN, Ford ME, Hatfull GF (March 1999). "Evolutionary relationships among diverse bacteriophages and prophages: all the world's a phage". Proceedings of the National Academy of Sciences of the United States of America. 96 (5): 2192–7. Bibcode:1999PNAS...96.2192H. doi:10.1073/pnas.96.5.2192. PMC 26759. PMID 10051617.
• Kitano H (March 2002). "Systems biology: a brief overview" (PDF). Science. 295 (5560): 1662–4. Bibcode:2002Sci...295.1662K. doi:10.1126/science.1069492. PMID 11872829.
• Ptashne, M. "A Genetic Switch: Phage Lambda Revisited", 3rd edition 2003
• Ptashne M (June 2005). "Regulation of transcription: from lambda to eukaryotes". Trends in Biochemical Sciences. 30 (6): 275–9. doi:10.1016/j.tibs.2005.04.003. PMID 15950866.
• Snyder, L. and Champness, W. "Molecular Genetics of Bacteria", 3rd edition 2007 (Contains an informative and well illustrated overview of bacteriophage lambda)
• Splasho, Online overview of lambda (illustrates genes active at all stages in lifecycle)

External links

• Life Cycle, Basic Animation of Lambda Lifecyecle (illustrates infection and lytic/lysogenic pathways with some protein and transcription detail)
• Time-lapse microscopy video from MIT showing both lysis and lysogeny by phage lambda
• Lambda Phage Life cycle (basic visual demonstration of Lambda bacteriophage life cycle)
• Lambda Phage genome in GenBank
• Lambda Phage Reference Proteome from UniProt
• Lambda Phage Protein Structures in NCBI (3D display of protein structures for bacteriophage Lambda)

UpToDate Contents

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• 1. 外科手術で使用される再建材料：分類および宿主応答 reconstructive materials used in surgery classification and host response
• 2. 血友病患者における第VIIIおよび第IX因子阻害物質 factor viii and factor ix inhibitors in patients with hemophilia
• 3. 遺伝子組換え第VIIa因子製剤：臨床使用、用量、副作用 recombinant factor viia clinical uses dosing and adverse effects
• 4. 造血細胞移植レシピエントにおけるヒトヘルペスウイルス6感染 human herpesvirus 6 infection in hematopoietic cell transplant recipients
• 5. 腫瘍壊死因子α阻害剤および抗酸菌感染 tumor necrosis factor alpha inhibitors and mycobacterial infections

English Journal

• Stromal cell-derived factor 1α-stimulated mesenchymal stem cells confer enhanced protection against light-induced retinal degeneration in rats.

• Xu W, Wang XT, Xu GX, Guo J, Huang LB.Author information Department of Ophthalmology, First Affiliated Hospital of Fujian Medical University Fuzhou , China , and.AbstractAbstract Purpose: Mesenchymal stem cells (MSCs) are currently considered to be modulators of repair in various tissues. After MSC transplant, photoreceptor rescue has been demonstrated in models of retinal degeneration. Herein, we evaluate the roles of MSCs in modulating the host reaction and photoreceptor preservation in rats suffering from light-induced retinal degeneration. Methods: Unstimulated and stromal cell-derived factor 1α (SDF-1α)-stimulated MSCs were intravenously transplanted into light-injured rats. Their photoreceptor rescue effect was compared with untreated light-injured rats and light-injured rats received only medium injection. Ciliary neurotrophic factor (CNTF) and glial fibrillary acidic protein (GFAP) expression was identified to assess host reaction post-transplantation. Retinal localization and integration of MSCs were determined by green fluorescence protein labeling. Results: MSCs were able to migrate and integrate into the host retina, and significantly inhibited retinal cell death. CNTF and GFAP were induced upregluation after MSC injection. SDF-1α stimulation elicited superior effects in both MSC migration and the inhibition of apoptosis. CNTF and GFAP expression in host retinas that received stimulated MSCs were stronger than in retinas that received unstimulated MSCs. Conclusions: Systemic administration of MSCs exerts a protective effect against light-induced retinal degeneration, and upregulates neurotrophin expression in the host retina. MSCs can be stimulated to enhance the therapeutic effect.
• Current eye research.Curr Eye Res.2014 Jan;39(1):69-78. doi: 10.3109/02713683.2013.824988. Epub 2013 Sep 27.
• Abstract Purpose: Mesenchymal stem cells (MSCs) are currently considered to be modulators of repair in various tissues. After MSC transplant, photoreceptor rescue has been demonstrated in models of retinal degeneration. Herein, we evaluate the roles of MSCs in modulating the host reaction and photor
• PMID 24074164

• Traditional Chinese medicine application in HIV: an in silico study.

• Huang HJ, Jian YR, Chen CY.Author information a Department of Chinese Pharmaceutical Sciences and Chinese Medicine Resources , China Medical University , Taichung , 40402 , Taiwan .AbstractViral infection by human immunodeficiency virus (HIV) requires integration of viral DNA with host DNA which involves the binding of HIV integrase (IN) with its co-factor lens epithelium-derived growth factor (LEDGF/p75). Since disrupted binding of IN with LEDGF/p75 inhibits proliferation of HIV, inhibition or denaturation of IN is a possible method for inhibiting HIV replication. D77 is a known drug with demonstrated inhibition against HIV by binding to IN. Herein, we utilized D77 as a control to screen for traditional Chinese medicine (TCM) compounds that exhibit similar atomic-level characteristics. 9-Hydroxy-(10E)-octadecenoic acid and Beauveriolide I were found to have higher Dock Scores to IN than D77 through virtual screening. Multiple linear regression (R2 = 0.9790) and support vector machine (R2 = 0.9114) models consistently predicted potential bioactivity of the TCM candidates against IN. The 40 ns molecular dynamics simulation showed that the TCM compounds fulfilled the drug-like criteria of forming stable complexes with IN. Atomic-level investigations revealed that 9-hydroxy-(10E)-octadecenoic acid bound to an important residue A:Lys173, and Beauveriolide I formed stable interactions with the core LEDGF binding site and with Asn256 of the IN binding site on LEDGF. The TCM candidates also initiated loss of α-helices that could affect the functionality of IN. Taken together, the ability of 9-hydroxy-(10E)-octadecenoic acid and Beauveriolide I to (1) form stable interactions affecting IN-LEDGF binding and (2) have predicted bioactivity against IN suggests that the TCM candidates might be potential starting structures for developing compounds that may disrupt IN-LEDGF binding. An animated interactive 3D complement (I3DC) is available in Proteopedia at http://proteopedia.org/w/Journal:JBSD:40.
• Journal of biomolecular structure & dynamics.J Biomol Struct Dyn.2014 Jan;32(1):1-12. doi: 10.1080/07391102.2012.745168. Epub 2012 Dec 20.
• Viral infection by human immunodeficiency virus (HIV) requires integration of viral DNA with host DNA which involves the binding of HIV integrase (IN) with its co-factor lens epithelium-derived growth factor (LEDGF/p75). Since disrupted binding of IN with LEDGF/p75 inhibits proliferation of HIV, inh
• PMID 23252879

• Impact of Hepatitis B Virus Integration Into Liver Tissue on the Efficacy of Peginterferon and Ribavirin Therapy in Hepatitis B Virus-negative Chronic Hepatitis C Patients.

• Toyoda H, Kumada T, Tada T, Murakami Y.Author information *Department of Gastroenterology, Ogaki Municipal Hospital, Ogaki †Center for Genomic Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan.AbstractBACKGROUND: Integration of hepatitis B virus (HBV) DNA into host hepatic DNA is found in patients without HBV surface antigen (HBsAg). We investigated the prevalence of HBV integration and its association with the outcome of peginterferon (PEG-IFN) and ribavirin combination therapy in HBsAg-negative chronic hepatitis C patients.
• Journal of clinical gastroenterology.J Clin Gastroenterol.2014 Jan;48(1):73-9. doi: 10.1097/MCG.0b013e31829c409d.
• BACKGROUND: Integration of hepatitis B virus (HBV) DNA into host hepatic DNA is found in patients without HBV surface antigen (HBsAg). We investigated the prevalence of HBV integration and its association with the outcome of peginterferon (PEG-IFN) and ribavirin combination therapy in HBsAg-negative
• PMID 23842217

Japanese Journal

• Lysogenisation of Shiga toxin-encoding bacteriophage represses cell motility

• The Journal of General and Applied Microbiology 64(1), 34-41, 2018
• NAID 130006565494

• 枯草菌SPβファージのIntegration/Excisionの制御機構

• 法政大学大学院紀要. 理工学・工学研究科編 = 法政大学大学院紀要. 理工学・工学研究科編 56, 2015-03-24
• NAID 120005616094

• ボルナ病ウイルスの神経病原性に関する研究

• ウイルス 65(1), 145-154, 2015
• NAID 130005128454

Related Pictures

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★リンクテーブル★

リンク元	「組込み宿主因子」「IHF」「host factor」
関連記事	「fact」「integration」「factor」「host」「host factor」

「組込み宿主因子」

　　[★]

英

integration host factor, IHF

関

[[]]

• DNA組込みに使われる細菌タンパク質

「IHF」

　　[★]

• 免疫性胎児水腫 immune hydrops fetalis
• integration host factor

「host factor」

　　[★]

宿主因子

関

integration host factor

「fact」

　　[★]

• n.

• 事実、現状、実際、実態

関

actual、actually、in fact、in practice、indeed、practically

　 　 　 　 　

「integration」

　　[★]

• n.

• 統合、組込み、(数学)積分

関

built-in、integral、integrate、integrative、unified、unify

　 　 　

「factor」

　　[★]

• n.

• 因子、要因、要素、ファクター

関

element、elementary、factorial、parameter

　 　 　 　 　 　 　

「host」

　　[★]

• 宿主、ホスト

　 　 　 　 　 　 　 　 　

「host factor」

　　[★]

宿主因子

関

integration host factor