| Summary: | In Saccharomyces cerevisiae, RTT107 (ESC4, YHR154W) encodes a BRCT-domain protein that is important for recovery from DNA damage during S phase. I have found that Rtt107 forms a complex with the Slx1/Slx4 structure-specific nuclease. Deletion of SLX4 confers many of the same phenotypes observed in rtt107∆, including DNA damage sensitivity, prolonged DNA damage checkpoint activation, and increased spontaneous DNA damage, suggesting that Slx4 and Rtt107 function in concert. These defects are not shared by Slx1 indicating that the function of Slx4 and Slx1 in the DNA damage response is not entirely overlapping. Furthermore, I found that Slx4 regulates the phosphorylation of Rtt107 by the checkpoint kinase Mec1.
The phenotypes conferred by deletion of RTT107 and the spectrum of its synthetic genetic interactions indicates that Rtt107 may function at stalled replication forks. I have shown that Rtt107 is recruited to chromatin in the presence of DNA damaging agents that cause DNA replication forks to stall. Recruitment of Rtt107 to chromatin requires Rtt109, an acetyltransferase, and the cullin Rtt101, but is not dependent on Slx4 or the checkpoint kinases. Rtt109 acetylates histone H3 on lysine 56 (H3-K56), yet recruitment of Rtt107 to chromatin does not require acetylation of H3-K56, indicating that Rtt109 may have additional targets. Chromatin immunoprecipitation indicates that the sites of Rtt107 binding correspond to regions at or near stalled replication forks throughout the genome. I propose that Rtt107 acts in the recovery from DNA damage by localizing to stalled replication forks and acting as a scaffold for assembly of DNA damage response proteins, ultimately promoting replication fork restart.
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