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the 9th letter of the Roman alphabet (同)i
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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）』「2014/08/06 16:40:52」(JST)

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DNA Polymerase I (or Pol I) is an enzyme that participates in the process of DNA replication. Discovered by Arthur Kornberg in 1956,^[1] it was the first known DNA polymerase (and, indeed, the first known of any kind of polymerase). It was initially characterized in E. coli, although it is ubiquitous in prokaryotes. In E. coli and many other bacteria, the gene that encodes Pol I is known as polA. The E. coli form of the enzyme is composed of 928 amino acids, and is an example of a processive enzyme - it can sequentially catalyze multiple polymerisations.

Pol I possesses four enzymatic activities:

A 5' -> 3' (forward) DNA-Dependent DNA polymerase activity, requiring a 3' primer site and a template strand
A 3' -> 5' (reverse) exonuclease activity that mediates proofreading
A 5' -> 3' (forward) exonuclease activity mediating nick translation during DNA repair.
A 5' -> 3' (forward) RNA-Dependent DNA polymerase activity. Pol I operates on RNA templates with considerably lower efficiency (0.1–0.4%) than it does DNA templates, and this activity is probably of only limited biological significance.^[2]

In the replication process, RNAse H removes the RNA primer (created by Primase) from the lagging strand and then Polymerase I fills in the necessary nucleotides between the Okazaki fragments (see DNA replication) in 5' -> 3' direction, proofreading for mistakes as it goes. It is a template-dependent enzyme - it only adds nucleotides that correctly base pair with an existing DNA strand acting as a template. DNA Ligase then joins the various fragments together into a continuous strand of DNA.

Despite its early characterisation, it quickly became apparent that Polymerase I was not the enzyme responsible for most DNA synthesis — DNA replication in E. coli proceeds at approximately 1,000 nucleotides/second, while the rate of base pair synthesis by Polymerase I averages only between 10 and 20 nucleotides/second. Moreover, its cellular abundance of approximately 400 molecules per cell did not correlate with the fact that there are typically only two replication forks in E. coli. Moreover, it is insufficiently processive to copy an entire genome, as it falls off after incorporating only 25-50 nucleotides. Its role in replication was proven when, in 1969, John Cairns isolated a viable Polymerase I mutant that lacked the polymerase activity.^[3] Cairns' lab assistant Paula De Lucia created thousands of cell free extracts from E.coli colonies and assayed them for DNA-polymerase activity. The 3,478th clone contained the polA mutant, which was named by Cairns to credit "Paula" [De Lucia].^[4] It was not until the discovery of DNA polymerase III that the main replicative DNA polymerase was finally identified.

Research applications

DNA polymerase I obtained from E. coli is used extensively for molecular biology research. However, the 5' -> 3' exonuclease activity makes it unsuitable for many applications. Fortunately this undesirable enzymatic activity can be simply removed from the holoenzyme to leave a useful molecule called the Klenow fragment, widely used in molecular biology. Exposure of DNA polymerase I to the protease subtilisin cleaves the molecule into a smaller fragment, which retains only the DNA polymerase and proofreading activities. 2313541.20.

References

^ Lehman IR, Bessman MJ, Simms ES, Kornberg A (July 1958). "Enzymatic synthesis of deoxyribonucleic acid. I. Preparation of substrates and partial purification of an enzyme from Escherichia coli". J. Biol. Chem. 233 (1): 163–70. PMID 13563462.
^ Ricchetti M, Buc H (February 1993). "E. coli DNA polymerase I as a reverse transcriptase". EMBO J. 12 (2): 387–96. PMC 413221. PMID 7679988.
^ De Lucia P, Cairns J (December 1969). "Isolation of an E. coli strain with a mutation affecting DNA polymerase". Nature 224 (5225): 1164–6. doi:10.1038/2241164a0. PMID 4902142.
^ Friedberg EC (February 2006). "The eureka enzyme: the discovery of DNA polymerase". Nat. Rev. Mol. Cell Biol. 7 (2): 143–7. doi:10.1038/nrm1787. PMID 16493419.

UpToDate Contents

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English Journal

The Selection of Recombinant Binary Plasmids Generated by Gateway(®) LR Cloning in the Escherichia coli Strain C2110.

Wu S, Zhao B.SourceDepartment of Horticulture, Virginia Polytechnic Institute and State University, Blacksburg, VA, 24061, USA, shuchi@vt.edu.
Molecular biotechnology.Mol Biotechnol.2013 Jun;54(2):125-32. doi: 10.1007/s12033-012-9548-1.
Gateway(®) cloning is widely used in molecular biology laboratories. Various binary vectors used for Agrobacterium-mediated plant transformation have been modified as destination vectors that are convenient for the sub-cloning of targeted genes from Entry plasmids. However, when the destination and
PMID 22555851

The HBx protein of hepatitis B virus confers resistance against nucleolar stress and anti-cancer drug-induced p53 expression.

Kapoor NR, Ahuja R, Shukla SK, Kumar V.SourceVirology Group, International Centre for Genetic Engineering and Biotechnology, Aruna Asaf Ali Marg, New Delhi 110067, India.
FEBS letters.FEBS Lett.2013 May 2;587(9):1287-92. doi: 10.1016/j.febslet.2013.03.004. Epub 2013 Mar 16.
The nucleolus is a stress sensor associated with cell cycle progression and a viral target. However, the role of the nucleolus during hepatitis B virus infection has not been studied. Here we show that under nucleolar stress, the HBx oncoprotein down-regulates p53 and p21(waf1) levels by disrupting
PMID 23507139

Bacterial DNA polymerases participate in oligonucleotide recombination.

Li XT, Thomason LC, Sawitzke JA, Costantino N, Court DL.SourceMolecular Control and Genetics Section, Gene Regulation and Chromosome Biology, Frederick National Laboratory for Cancer Research, Frederick, MD, 21702, USA.
Molecular microbiology.Mol Microbiol.2013 May 2. doi: 10.1111/mmi.12231. [Epub ahead of print]
Synthetic single-strand oligonucleotides (oligos) with homology to genomic DNA have proved to be highly effective for constructing designed mutations in targeted genomes, a process referred to as recombineering. The cellular functions important for this type of homologous recombination have yet to b
PMID 23634873

Japanese Journal

ヒステリシス素子で結合された区分線形発振器の同期現象について (回路とシステム)

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NAID 40020650121

8個の発振器で構築された4本の梯子を十字型に結合した系でみられる個別に動く位相反転波 (回路とシステム)

電子情報通信学会技術研究報告 = IEICE technical report : 信学技報 115(239), 109-114, 2015-10-05
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van der Pol発振器を環状にインダクタによって結合した系にみられる複雑な振る舞いをする波の調査 (回路とシステム)

電子情報通信学会技術研究報告 = IEICE technical report : 信学技報 115(239), 103-108, 2015-10-05
NAID 40020650112

Related Pictures

★リンクテーブル★

リンク元	「Klenow fragment」「DNA polymerase alpha」「RNA polymerase I」
拡張検索	「Pol III」「Pol II」「PolII」
関連記事	「I」「Pol」「P」「Id」「Po」

「Klenow fragment」

DNA polymerase I
	Functional domains in the Klenow Fragment (left) and DNA Polymerase I (right).
Identifiers
Organism	Escherichia coli; (str. K-12 substr. MG1655)
Symbol	polA
Entrez	948356
PDB	1DPI
RefSeq (Prot)	NP_418300.1
UniProt	P00582
Other data
EC number	2.7.7.7
Chromosome	genome: 4.04 - 4.05 Mb