PT - JOURNAL ARTICLE AU - Rattray, Alison J. AU - McGill, Carolyn B. AU - Shafer, Brenda K. AU - Strathern, Jeffrey N. TI - Fidelity of Mitotic Double-Strand-Break Repair in <em>Saccharomyces cerevisiae:</em> A Role for <em>SAE2</em>/<em>COM1</em> DP - 2001 May 01 TA - Genetics PG - 109--122 VI - 158 IP - 1 4099 - http://www.genetics.org/content/158/1/109.short 4100 - http://www.genetics.org/content/158/1/109.full SO - Genetics2001 May 01; 158 AB - Errors associated with the repair of DNA double-strand breaks (DSBs) include point mutations caused by misincorporation during repair DNA synthesis or novel junctions made by nonhomologous end joining (NHEJ). We previously demonstrated that DNA synthesis is ∼100-fold more error prone when associated with DSB repair. Here we describe a genetic screen for mutants that affect the fidelity of DSB repair. The substrate consists of inverted repeats of the trp1 and CAN1 genes. Recombinational repair of a site-specific DSB within the repeat yields TRP1 recombinants. Errors in the repair process can be detected by the production of canavanine-resistant (can1) mutants among the TRP1 recombinants. In wild-type cells the recombinational repair process is efficient and fairly accurate. Errors resulting in can1 mutations occur in &lt;1% of the TRP1 recombinants and most appear to be point mutations. We isolated several mutant strains with altered fidelity of recombination. Here we characterize one of these mutants that revealed an ∼10-fold elevation in the frequency of can1 mutants among TRP1 recombinants. The gene was cloned by complementation of a coincident sporulation defect and proved to be an allele of SAE2/COM1. Physical analysis of the can1 mutants from sae2/com1 strains revealed that many were a novel class of chromosome rearrangement that could reflect break-induced replication (BIR) and NHEJ. Strains with either the mre11s-H125N or rad50s-K81I alleles had phenotypes in this assay that are similar to that of the sae2/com1Δ strain. Our data suggest that Sae2p/Com1p plays a role in ensuring that both ends of a DSB participate in a recombination event, thus avoiding BIR, possibly by regulating the nuclease activity of the Mre11p/Rad50p/Xrs2p complex.