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the 9th letter of the Roman alphabet (同)i
the 16th letter of the Roman alphabet (同)p
a European river; flows into the Adriatic Sea (同)Po River

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/07/29 16:27:50」(JST)

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Schematic picture of DNA polymerase III* (with subunits).

Pol III can also refer to HNoMS Pol III, a Norwegian guard vessel from WWII

DNA polymerase III holoenzyme is the primary enzyme complex involved in prokaryotic DNA replication. It was discovered by Thomas Kornberg (son of Arthur Kornberg) and Malcolm Gefter in 1970. The complex has high processivity (i.e. the number of nucleotides added per binding event) and, specifically referring to the replication of the E.coli genome, works in conjunction with four other DNA polymerases (Pol I, Pol II, Pol IV, and Pol V). Being the primary holoenzyme involved in replication activity, the DNA Pol III holoenzyme also has proofreading capabilities that correct replication mistakes by means of exonuclease activity working 3'→5'. DNA Pol III is a component of the replisome, which is located at the replication fork.

Components

The replisome is composed of the following:

2 DNA Pol III enzymes, each comprising α, ε and θ subunits. (It has been proven that there is a third copy of Pol III at the replisome.^[1])
- the α subunit (encoded by the dnaE gene) has the polymerase activity.
- the ε subunit (dnaQ) has 3'→5' exonuclease activity.
- the θ subunit (holE) stimulates the ε subunit's proofreading.
2 β units (dnaN) which act as sliding DNA clamps, they keep the polymerase bound to the DNA.
2 τ units (dnaX) which acts to dimerize two of the core enzymes (α, ε, and θ subunits).
1 γ unit (also dnaX) which acts as a clamp loader for the lagging strand Okazaki fragments, helping the two β subunits to form a unit and bind to DNA. The γ unit is made up of 5 γ subunits which include 3 γ subunits, 1 δ subunit (holA), and 1 δ' subunit (holB). The δ is involved in copying of the lagging strand.
Χ (holC) and Ψ (holD) which form a 1:1 complex and bind to γ or τ.^[2]

Activity

DNA polymerase III synthesizes base pairs at a rate of around 1000 nucleotides per second.^[3] DNA Pol III activity begins after strand separation at the origin of replication. Because DNA synthesis cannot start de novo, an RNA primer, complementary to part of the single-stranded DNA, is synthesized by primase (an RNA polymerase):

("!" for RNA, '"$" for DNA, "*" for polymerase)

--------> 
         * * * *
! ! ! !  _ _ _ _    
_ _ _ _ | RNA   |   <--ribose (sugar)-phosphate backbone
G U A U | Pol   |   <--RNA primer
* * * * |_ _ _ _|   <--hydrogen bonding
C A T A G C A T C C <--template ssDNA (single-stranded DNA)
_ _ _ _ _ _ _ _ _ _ <--deoxyribose (sugar)-phosphate backbone
$ $ $ $ $ $ $ $ $ $

Addition onto 3'OH

As replication progresses and the replisome moves forward, DNA polymerase III arrives at the RNA primer and begins replicating the DNA, adding onto the 3'OH of the primer:

         * * * *
! ! ! !  _ _ _ _
_ _ _ _ | DNA   |   <--ribose (sugar)-phosphate backbone
G U A U | Pol   |   <--RNA primer
* * * * |_III_ _|   <--hydrogen bonding
C A T A G C A T C C <--template ssDNA (single-stranded DNA)
_ _ _ _ _ _ _ _ _ _ <--deoxyribose (sugar)-phosphate backbone
$ $ $ $ $ $ $ $ $ $

Synthesis of DNA

DNA polymerase III will then synthesize a continuous or discontinuous strand of DNA, depending if this is occurring on the leading or lagging strand (Okazaki fragment) of the DNA. DNA polymerase III has a high processivity and therefore, synthesizes DNA very quickly. This high processivity is due in part to the β-clamps that "hold" onto the DNA strands.

        ----------->
                    * * * *
! ! ! ! $ $ $ $ $ $ _ _ _ _
_ _ _ _ _ _ _ _ _ _| DNA   |   <--deoxyribose (sugar)-phosphate backbone
G U A U C G T A G G| Pol   |   <--RNA primer
* * * * * * * * * *|_III_ _|   <--hydrogen bonding
C A T A G C A T C C <--template ssDNA (single-stranded DNA)
_ _ _ _ _ _ _ _ _ _ <--deoxyribose (sugar)-phosphate backbone
$ $ $ $ $ $ $ $ $ $

Removal of primer

After replication of the desired region, the RNA primer is removed by DNA polymerase I via the process of nick translation. The removal of the RNA primer allows DNA ligase to ligate the DNA-DNA nick between the new fragment and the previous strand. DNA polymerase I & III, along with many other enzymes are all required for the high fidelity, high-processivity of DNA replication.

References

^ DOI: 10.1126/science.1185757
^ Olson MW, Dallmann HG, McHenry CS (December 1995). "DnaX complex of Escherichia coli DNA polymerase III holoenzyme. The chi psi complex functions by increasing the affinity of tau and gamma for delta.delta' to a physiologically relevant range". J. Biol. Chem. 270 (49): 29570–7. PMID 7494000.
^ Kelman Z, O'Donnell M (1995). "DNA polymerase III holoenzyme: structure and function of a chromosomal replicating machine". Annu. Rev. Biochem. 64: 171–200. doi:10.1146/annurev.bi.64.070195.001131. PMID 7574479.

External links

Overview at Oregon State University
DNA Polymerase III at the US National Library of Medicine Medical Subject Headings (MeSH)

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English Journal

Why should cancer biologists care about tRNAs? tRNA synthesis, mRNA translation and the control of growth.

Grewal SS1.
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Alisporivir with peginterferon/ribavirin in patients with chronic hepatitis C genotype 1 infection who failed to respond to or relapsed after prior interferon-based therapy: FUNDAMENTAL, a Phase II trial.

Buti M1, Flisiak R2, Kao JH3, Chuang WL4, Streinu-Cercel A5, Tabak F6, Calistru P7, Goeser T8, Rasenack J9, Horban A10, Davis GL11, Alberti A12, Mazzella G13, Pol S14, Orsenigo R15, Brass C15.
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miRNA-embedded shRNAs for lineage-specific BCL11A knockdown and hemoglobin F induction.

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Japanese Journal

アデノウイルスベクターの最近の進展：VA欠失ベクターを中心に

近藤小貴,前川文,斎藤泉,鐘ヶ江裕美
ウイルス 63(2), 155-164, 2013
… の炎症については，原因ウイルスタンパク質の同定に成功し，この問題を解決した「低炎症型ベクター」を報告した．しかし，究極のFG-AdVを考えた時，残存しているアデノウイルスゲノム領域からPol IIIにより発現している2種類のウイルス随伴RNA (VA RNA)の欠失が必要である．VA RNAはウイルス増殖に必須では無いものの，ウイルス増殖に適した環境を整備する役割を担っており，特に感染後期に大量に …
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Regulation of Pol Ⅰ-Transcribed 45S rDNA and Pol Ⅲ-Transcribed 5S rDNA in Arabidopsis

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Use of Bombyx mori U6 Promoter for Inducing Gene-Silencing in Silkworm Cells

Ohtsuka Daisuke,Nakatsukasa Tomonori,Fujita Ryosuke,Asano Shin-ichiro,Sahara Ken,Bando Hisanori
Journal of Insect Biotechnology and Sericology 77(3), 3_125-2_131, 2008
… Studies on pol III promoter-based expression systems have been well documented showing them to be an effective tool for inducing RNAi in mammalian cells and Drosophila Schneider 2 (S2) cells, but not in silkworm cells. …
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Related Pictures

★リンクテーブル★

リンク元	「RNAポリメラーゼIII」「DNA polymerase delta」
拡張検索	「Pol IIIホロ酵素」
関連記事	「II」「I」「Pol」「P」「Po」