ons of WRN could be an important mechanism for the regulation of WRN functions in response to DNA damage. Acetylation is one of Acetylation Enhances WRN the most important post-translational modifications for efficient DNA repair. Histone acetylation regulates chromatin assembly facilitating access of DNA repair proteins to the sites of DNA lesions. Histone acetyltransferase, p300, can also acetylate and interact with several DNA repair proteins; the events modulate their activity, protein interactions and cellular localization. This study provides the first evidence that p300 acetylation of WRN stimulates its catalytic activities in vitro and in vivo and may play a key role in regulating its function in LP BER. Here, a mechanistic basis for the effect of acetylation on WRN function was characterized in detail. This study confirms an important role for WRN in BER, 24658113 and a specific role for p300 acetylation in regulating WRN function during the course of BER. It was previously shown that WRN participates in the repair 19380825 of MMS induced DNA base damage via both short patch and LP BER. The present study demonstrates that alkylation damage strongly stimulates acetylation of WRN, and that acetylation of WRN by p300 stimulates its catalytic activities that stimulate pol b-mediated strand displacement DNA synthesis and LP BER. Furthermore, treatment of wild type and WRN KD cells with sodium butyrate stimulates LP BER in wild type cells but not in WRN KD cells. These data strongly support the ideas that p300 acetylation of WRN is an important step in regulating BER in cells with DNA damage. WRN plays a role in BER during the repair of certain lesions. It can unwind several BER Clemizole hydrochloride chemical information intermediates such as single-strand break intermediates, and stimulate pol b strand displacement DNA synthesis via its helicase activity. Since pol b does not have an intrinsic editing function, it makes frequent Acetylation Enhances WRN errors during nucleotide incorporation. The exonuclease domain of WRN has proofreading activity that can remove 39 mismatches following misincorporation of nucleotides by pol b, 
and thus potentially enhance the fidelity of BER. It is likely that WRN exonuclease and helicase activities facilitate pol b mediated strand displacement and accuracy of BER. Strong acetylation of WRN after alkylation damage might enhance the fidelity of DNA repair synthesis. In vitro studies with reconstituted nucleosome core particles suggest that highly condensed chromatin inhibits some steps in BER. In particular, uracil DNA glycosylase and AP endonuclease activities are approximately 10-fold lower in chromatin than in ��naked��DNA, and pol b-catalyzed DNA synthesis is completely inhibited by nucleosomes in vitro, but DNA ligase I and Fen-1 are not inhibited by nucleosomes in vitro . These data suggest that pol b-catalyzed DNA synthesis may be the rate-limiting step in BER in vivo, and that the major point of restriction of BER in chromatin is the synthesis step of pol b. This indicates that increased acetylation might facilitate recovery from alkylation DNA damage by two distinct complementing mechanisms. Firstly, acetylation of histones might promote chromatin decondensation. Secondly, acetylation of BER proteins, including WRN, might specifically stimulate LP BER. The results presented here support the latter possibility, demonstrating that WRN acetylation stimulates pol b-mediated strand displacement DNA synthesis and LP BER. It is also possible that acetylated W
