Genetic Requirements for RAD51- andRAD54-Independent Break-Induced Replication Repair of a Chromosomal Double-Strand Break

Abstract

Broken chromosomes can be repaired by several homologous recombination mechanisms, including gene conversion and break-induced replication (BIR). In Saccharomyces cerevisiae, an HO endonuclease-induced double-strand break (DSB) is normally repaired by gene conversion. Previously, we have shown that in the absence ofRAD52, repair is nearly absent and diploid cells lose the broken chromosome; however, in cells lacking RAD51, gene conversion is absent but cells can repair the DSB by BIR. We now report that gene conversion is also abolished when RAD54, RAD55, and RAD57 are deleted but BIR occurs, as withrad51Δ cells. DSB-induced gene conversion is not significantly affected when RAD50, RAD59, TID1(RDH54), SRS2, or SGS1 is deleted. Various double mutations largely eliminate both gene conversion and BIR, including rad51Δ rad50Δ, rad51Δ rad59Δ, andrad54Δ tid1Δ. These results demonstrate that there is aRAD51- and RAD54-independent BIR pathway that requires RAD59, TID1, RAD50, and presumablyMRE11 and XRS2. The similar genetic requirements for BIR and telomere maintenance in the absence of telomerase also suggest that these two processes proceed by similar mechanisms.

ACKNOWLEDGMENTS

We thank Carol Greider and members of the Haber lab for their comments and suggestions. Qijun Chen and Carol Greider kindly providedrad59Δ strains, and we obtained plasmids from Ralph Keil, David Schild, Susan Lovett and Frédéric Pâques.

H.K. was supported by National Institutes of Health grant GM53738. J.E.H. was supported by National Institutes of Health grant GM20056 and National Science Foundation grant MCB-9724086. M.L.N. was a Howard Hughes Medical Institute undergraduate summer research scholar at Brandeis University.

L.S., A.M., and M.L.N. made equal contributions to this work.