The failure of cells to repair damaged DNA can result in genomic instability and cancer. To efficiently repair chromosomal DNA lesions, the repair machinery must gain access to the damaged DNA in the context of chromatin. Here we report that both the RSC and Swi/Snf ATP-dependent chromatin-remodeling complexes play key roles in double-strand break (DSB) repair, specifically by homologous recombination (HR). RSC and Swi/ Snf are each recruited to an in vivo DSB site but with distinct kinetics. We show that Swi/Snf is required earlier, at or preceding the strand invasion step of HR, while RSC is required following synapsis for completion of the recombinational repair event.Supplemental material is available at http://www.genesdev.org.

RSC is a 15-protein ATP-dependent chromatin-remodeling complex related to Snf-Swi, the prototypical ATP-dependent nucleosome remodeler in budding yeast. Despite insight into the mechanism by which purified RSC remodels nucleosomes, little is known about the chromosomal targets or cellular pathways in which RSC acts. To better understand the cellular function of RSC, a screen was undertaken for gene dosage suppressors of sth1-3ts, a temperature-sensitive mutation in STH1, which encodes the essential ATPase subunit. Slg1p and Mid2p, two type I transmembrane stress sensors of cell wall integrity that function upstream of protein kinase C (Pkc1p), were identified as multicopy suppressors of sth1-3ts cells. Although the sth1-3ts mutant exhibits defects characteristic of PKC1 pathway mutants (caffeine and staurosporine sensitivities and an osmoremedial phenotype), only upstream components and not downstream effectors of the PKC1-MAP kinase pathway can suppress defects conferred by sth1-3ts, suggesting that RSC functions in an alternative PKC1-dependent pathway. Moreover, sth1-3ts cells display defects in actin cytoskeletal rearrangements and are hypersensitive to the microtubule depolymerizing drug, TBZ; both of these defects can be corrected by the high-copy suppressors. Together, these data reveal an important functional connection between the RSC remodeler and PKC1-dependent signaling in regulating the cellular architecture.