loop by pairing on the homologous noncontiguous sequence [44]. Since we observed in cells experiencing exogenous oxidative stress a correlation between absence of Sty1 dependent Rad52 phosphorylation and persistence of Rad52 foci, it might be that lower levels of rearrangements at blocked replication forks as well as reduced spontaneous gene conversion in sty1-d cells result from incapacity to form a stable D loop. According to this hypothesis, a Sty1 dependent phosphorylation of Rad52 should occur also in cells not exposed to oxidants, however it might be difficult to detect it because of low basal levels of HR. Consistently, we didn’t observed Rad52 phosphorylation using the RuraR system where one replication fork per cell is blocked (not shown). Alternatively, Rad52 phosphorylation by Sty1 occurs only upon Sty1 activation by oxidative stress while basal levels of Sty1 affect spontaneous HR and HR at blocked replication forks without Rad52 modification. 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(2008) Inhibition of S-phase progression triggered by UVA-induced ROS does not PLOS ONE | www.plosone.org 11 October 2012 | Volume 7 | Issue 10 | e47987