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RecA - dependent recovery of arrested DNA replication forks

RecA - dependent recovery of arrested DNA replication forks . 2012-10-30 Chi Zhang Qiping Lu. Annu. Rev. Genet. 2003. 37:611–46 doi : 10.1146/annurev.genet.37.110801.142616. Replication forks’ hurdles. abasic sites from spontaneous depurination

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RecA - dependent recovery of arrested DNA replication forks

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  1. RecA-dependent recovery of arrested DNA replication forks 2012-10-30 Chi Zhang Qiping Lu Annu. Rev. Genet. 2003. 37:611–46 doi: 10.1146/annurev.genet.37.110801.142616

  2. Replication forks’ hurdles • abasicsites from spontaneous depurination • oxidative lesions such as thymine glycol and 8-oxo-guanine • bulky chemical DNA adducts • photoproducts due to UV exposure • interstrand DNA crosslinks • ionizing radiation break single&double strand DNA

  3. UV irradiation lesions • cis, syn-cyclobutanepyrimidine dimer (CPD) • pyrimidine-6-4-pyrimidone photoproduct (6-4 PP)

  4. Other Key Genes • LexArepressor • uvrA, uvrB, and uvrC • ydjQ(now termed cho) • polB, dinB, and umuCplus umuD

  5. Regulation of SOS genes by RecA/LexA

  6. Recovery by Recombination

  7. Questions remained…

  8. Question # 1 If recA did promote DNA repair by recombination, it certainly did not operate with high efficiency in the absence of uvrA Although RecA promoted limited survival in uvrA mutants, the survival of cells synergistically increased in the presence of excision repair.

  9. Question # 2 Observation: Replication was strongly inhibited by UV-induced DNA lesions, that the inhibition was more severe, and that replication failed to significantly recover in either recA or uvrA mutants. Prediction from the recombinational model: Replication should continue at normal or near-normal rates through the lesion-containing parental DNA, leaving gaps at the lesion sites.

  10. Question # 3 Observation: Whenever significant levels of strand exchanges were detected in populations of cells, there was a corresponding high level of cell death and mutagenesis. Prediction from the recombinational model: In the presence of DNA damage, the more strand exchanges that occur, the better off the cell should be.

  11. Model is revised Repair-by-recombination model Repair-without-recombination model: RecA simply maintains the fork until replication can resume.

  12. Recovery without Recombination

  13. Recovery without Recombination

  14. Experiments to support the model

  15. Concluding remarks RecA was originally discovered as a gene required to change the genetic information during sexual cell cycles. Now research have revealed that it is also the key enzyme required to maintain the genetic information when DNA damage is encountered during replication in asexual cell cycles.

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