UC Davis

The Mre11-Rad50-Xrs2/NBS1 (MRX/N) nuclease/ATPase complex plays structural and catalytic roles in the repair of DNA double-strand breaks (DSBs) and is the DNA damage sensor for Tel1/ATM kinase activation. Saccharomyces cerevisiae Sae2 can function with MRX to initiate 5'-3' end resection and also plays an important role in attenuation of DNA damage signaling. Here we describe a class of mre11 alleles that suppresses the DNA damage sensitivity of sae2Δ cells by accelerating turnover of Mre11 at DNA ends, shutting off the DNA damage checkpoint and allowing cell cycle progression. The mre11 alleles do not suppress the end resection or hairpin-opening defects of the sae2Δ mutant, indicating that these functions of Sae2 are not responsible for DNA damage resistance. The purified M(P110L)RX complex shows reduced binding to single- and double-stranded DNA in vitro relative to wild-type MRX, consistent with the increased turnover of Mre11 from damaged sites in vivo. Furthermore, overproduction of Mre11 causes DNA damage sensitivity only in the absence of Sae2. Together, these data suggest that it is the failure to remove Mre11 from DNA ends and attenuate Rad53 kinase signaling that causes hypersensitivity of sae2Δ cells to clastogens.