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Brad Therad1

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Last Updated: 02 July 2021

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Cellular DNA is damaged continuously by a variety of endogenous and exogenous factors. Abasic sites arise in DNA frequently AS result of spontaneous hydrolysis of N-glycosylic bond and AS intermediates following removal of damage bases by DNA glycosylases. Oxygen free radicals, generated from normal cellular metabolism or from oxidative stress resulting from exposure of cells to DNA damaging agents such AS H 2 O 2 and ionizing radiation, can attack DNA AT either sugar or base. Attack AT sugar can cause sugar fragmentation, yielding strand break with 3-terminal fragment deoxyribose moiety. Strand breaks formed in this manner usually have 3-phosphate or 3-phosphoglycolate AT terminus, which present block to repair synthesis by DNA polymerases. Free radical attack on purines and pyrimidines in DNA produces a variety of damage bases, AS for example, 8-oxoguanine and thymine glycol, which are removed by action of specific DNA glycosylases such AS Ogg1 and Ntg1 and Ntg2, respectively. In addition to DNA glycosylase activity, these enzymes also harbor AP lyase activity that can incise DNA on 3 sides of the AP site, yielding 3 terminus with an,-unsaturated aldehyde, 4 R-4hydroxy-trans-2pentenal moiety, which, too, is blocked to synthesis by DNA polymerases. In Saccharomyces cerevisiae, Apn1 and Apn2, which possess class II AP endonuclease activity and also 3-phosphodiesterase activity, function in removal of AP sites AS well AS in removal of 3-PG, 3-dRP, and other such 3-blocking groups. Apn1, which shares extensive homology with Escherichia coli endonuclease IV, is major AP endonuclease in yeast, accounting for > 90 % of this activity in yeast cells, and it also has 3-phosphodiesterase activity. Apn2, which shares extensive homology with E. Coli exonuclease III and with human Ape1 and Ape2 proteins, accounts for < 10 % of AP endonuclease activity in yeast. In addition to AP endonuclease activity, Apn2 displays robust 5-phosphodiesterase activity, and this activity, but not AP endonuclease activity, is further stimulated by proliferating cell nuclear antigen. Apn1, Apn2, and nucleotide excision repair constitute alternate pathways for removal of AP sites in yeast. The NER system is highly conserved among eukaryotes. In S. Cerevisiae, combination of Rad14, Rad4-Rad23, RPA, TFIIH, RAD1-RAD10, and Rad2 and in humans, combination of their respective counterparts XPA, XPC-HR23B, RPA, TFIIH, XPF-ERCC1, and XPG mediate dual incision of damage DNA strand, resulting in release of 30-nt lesion-containing DNA fragment. Yeast Rad14 and Rad4-Rad23 proteins act AT damage recognition step, and following unwinding of duplex DNA by Rad3 and Rad25 DNA helicase subunits of TFIIH, RAD1-RAD10 and Rad2 nucleases incise damage strand on 5-and 3-side of lesion, respectively.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

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* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

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