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block the action of
put down by force or intimidation; "The government quashes any attempt of an uprising"; "China keeps down her dissidents very efficiently"; "The rich landowners subjugated the peasants working the land" (同)quash, keep_down, subdue, subjugate, reduce
any of a large group of nitrogenous organic compounds that are essential constituents of living cells; consist of polymers of amino acids; essential in the diet of animals for growth and for repair of tissues; can be obtained from meat and eggs and milk and legumes; "a diet high in protein"
an agent that represses (同)represser

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〈暴動など〉‘を'抑圧する,鎮圧する / 〈感情など〉‘を'抑える / 〈不安・いやな記憶など〉‘を'抑圧する(意識しないようにすること)
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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/08/04 14:39:09」(JST)

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1: RNA Polymerase, 2: Repressor, 3: Promoter, 4: Operator, 5: Lactose, 6: lacZ, 7: lacY, 8: lacA. Top: The gene is essentially turned off. There is no lactose to inhibit the repressor, so the repressor binds to the operator, which obstructs the RNA polymerase from binding to the promoter and making lactase. Bottom: The gene is turned on. Lactose is inhibiting the repressor, allowing the RNA polymerase to bind with the promoter, and express the genes, which synthesize lactase. Eventually, the lactase will digest all of the lactose, until there is none to bind to the repressor. The repressor will then bind to the operator, stopping the manufacture of lactase.

In molecular genetics, a repressor is a DNA- or RNA-binding protein that inhibits the expression of one or more genes by binding to the operator or associated silencers. A DNA-binding repressor blocks the attachment of RNA polymerase to the promoter, thus preventing transcription of the genes into messenger RNA. An RNA-binding repressor binds to the mRNA and prevents translation of the mRNA into protein. This blocking of expression is called repression.

Function

If an inducer, a molecule that initiates the gene expression, is present, then it can interact with the repressor protein and detach it from the operator. RNA polymerase then can transcribe the message (expressing the gene). A corepressor is a molecule that can bind to repressor and make it bind to the operator tightly, which decreases transcription. A repressor that binds with a corepressor is termed an aporepressor or inactive repressor. One type of aporepressor is the trp repressor, an important metabolic protein in bacteria.

The above mechanism of repression is a type of a feedback mechanism because it only allows transcription to occur if a certain condition is present: the presence of specific inducer(s). Within the Eukaryotic genome are regions of DNA known as silencers. These DNA sequences bind to repressors to partially or fully repress the expression of a gene. Silencers can be located several bases upstream or downstream from the actual promoter of the gene. Repressors can also have two binding sites: one for the silencer region and one for the promoter. This causes chromosome looping allowing the promoter region and the silencer region to come to close proximity.

Examples

lac operon

lacZYA transcribes the proteins needed for lactose breakdown.^[1] lacI synthesizes the repressor of the lacZYA gene.^[1] The gene lacI is situated immediately upstream of lacZYA but is transcribed from a different promoter.^[1] The lacI gene synthesizes LacI repressor protein. The LacI repressor protein represses lacZYA by binding to the operator sequence lacO.^[1]

The lacZYA repressor is constitutively expressed. It is always bound to the operator region of the promoter which interferes with the ability of RNA polymerase (RNAP) begin transcription of the lacZYA operon.^[1] In the presence of the inducer allolactose, the repressor changes conformation and falls off the operator. RNAP is then able to bind to the promoter and begin transcription of the lacZYA gene.^[1]

met operon

An example of a repressor protein is the methionine repressor MetJ. MetJ interacts with DNA bases via a pair of α-helices. MetJ is a homodimer consisting of two monomers, which each provides a beta ribbon and an alpha helix. Together, the beta ribbons of each monomer come together to form an antiparallel beta-sheet which binds to the DNA operator ("Met box") in its major groove. Once bound, the MetJ dimer interacts with another MetJ dimer bound to the complementary strand of the operator via its alpha helices. AdoMet binds to a pocket in MetJ that does not overlap the site of DNA binding.

The Met box has the sequence AGACGTCT which is a palindrome (it shows dyad symmetry) allowing the same sequence to be recognised on either strand of the DNA. The junction between C and G in the middle of the Met box contains a pyrimidine-purine step that becomes positively supercoiled forming a kink in the phosphodiester backbone. This is how the protein checks for the recognition site as it allows the DNA duplex to follow the shape of the protein. In other words, recognition happens through indirect readout of the structural parameters of the DNA, rather than via specific base sequence recognition.

Each MetJ dimer contains two binding sites for the cofactor S-Adenosyl methionine (SAM) which is a product in the biosynthesis of methionine. When SAM is present it binds to the MetJ protein increasing its affinity for its cognate operator site which halts transcription of genes involved in methionine synthesis. When SAM concentration becomes low the repressor dissociates from the operator site allowing more methionine to be produced.

References

^ ^a ^b ^c ^d ^e ^f Slonczewski, Joan, and John Watkins. Foster. Microbiology: An Evolving Science. New York: W.W. Norton &, 2009. Print.

External links

Repressor Proteins at the US National Library of Medicine Medical Subject Headings (MeSH)

UpToDate Contents

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English Journal

CHD8short, a naturally-occurring truncated form of a chromatin remodeler lacking the helicase domain, is a potent transcriptional coregulator.

Kunkel GR1, Tracy JA2, Jalufka FL2, Lekven AC3.
Gene.Gene.2018 Jan 30;641:303-309. doi: 10.1016/j.gene.2017.10.058. Epub 2017 Oct 25.
PMID 29079199

CRHR2/Ucn2 signaling is a novel regulator of miR-7/YY1/Fas circuitry contributing to reversal of colorectal cancer cell resistance to Fas-mediated apoptosis.

Pothoulakis C1, Torre-Rojas M2, Duran-Padilla MA3, Gevorkian J1, Zoras O4, Chrysos E4, Chalkiadakis G4, Baritaki S1,4.
International journal of cancer.Int J Cancer.2018 Jan 15;142(2):334-346. doi: 10.1002/ijc.31064. Epub 2017 Oct 12.
PMID 28929494

Tumor-suppressive miR-145 co-repressed by TCF4-β-catenin and PRC2 complexes forms double-negative regulation loops with its negative regulators in colorectal cancer.

Wang W1, Xiao X2, Chen X1, Huo Y1,3, Xi WJ1, Lin ZF1, Zhang D1, Li YF1,3, Yang F1, Wen WH1, Yang AG1, Wang T1,3.
International journal of cancer.Int J Cancer.2018 Jan 15;142(2):308-321. doi: 10.1002/ijc.31056. Epub 2017 Oct 3.
PMID 28921929

Japanese Journal

A novel N-terminal motif is responsible for the evolution of neural crest-specific gene-regulatory activity in vertebrate FoxD3

Ono Hiroki,Kozmik Zbynek,Yu Jr-Kai,Wada Hiroshi,和田洋
Developmental biology 385(2), 396-404, 2014-01
… Here, to investigate the role of protein evolution in the emergence of the neural crest GRN, we examined the neural crest cell (NCC) differentiation-inducing activity of chordate FoxD genes. … Amphioxus and vertebrate (Xenopus) FoxD proteins both exhibited transcriptional repressor activity in Gal4 transactivation assays and bound to similar DNA sequences in vitro. …
NAID 120005396072

VP16 fusion efficiently reveals the function of transcriptional repressors in Arabidopsis

Fujiwara Sumire,Kigoshi Keiko,Mitsuda Nobutaka,Suzuki Kaoru,Ohme-Takagi Masaru
Plant Biotechnology, 2014
… Thus, aiming for searching clues to understand their functions, we generated transgenic plants in which a putative transcriptional repressor fused with a VP16 viral trans-activation domain was expressed constitutively. … Several plants with strong morphological phenotypes such as leaf and flower development defects were isolated from those lines expressing potential transcriptional repressors with unknown functions, giving the clue to reveal the yet-to-be analyzed functions of each protein. …
NAID 130003391373