Brc1-Mediated DNA Repair and Damage Tolerance

Abstract

The structural maintenance of chromosome (SMC) proteins are key elements in controlling chromosome dynamics. In eukaryotic cells, three essential SMC complexes have been defined: cohesin, condensin, and the Smc5/6 complex. The latter is essential for DNA damage responses; in its absence both repair and checkpoint responses fail. In fission yeast, the UV-C and ionizing radiation (IR) sensitivity of a specific hypomorphic allele encoding the Smc6 subunit, rad18-74 (renamed smc6-74), is suppressed by mild overexpression of a six-BRCT-domain protein, Brc1. Deletion of brc1 does not result in a hypersensitivity to UV-C or IR, and thus the function of Brc1 relative to the Smc5/6 complex has remained unclear. Here we show that brc1D cells are hypersensitive to a range of radiomimetic drugs that share the feature of creating lesions that are an impediment to the completion of DNA replication. Through a genetic analysis of brc1D epistasis and by defining genes required for Brc1 to suppress smc6-74, we find that Brc1 functions to promote recombination through a novel postreplication repair pathway and the structure-specific nucleases Slx1 and Mus81. Activation of this pathway through overproduction of Brc1 bypasses a repair defect in smc6-74, reestablishing resolution of lesions by recombination.

Mms22 Preserves Genomic Integrity During DNA Replication in Schizosaccharomyces pombe

“…On the basis of putative interaction between budding yeast Mms22p and Rtt107p (Ho et al 2002;Chin et al 2006), we hypothesized that if mms22 1 is the ortholog of MMS22, then mms22 and brc1 should show genetic epistasis if the two proteins function exclusively together. We observed that brc1D mutants grow with wild-type kinetics, but are sensitive to the same spectrum of DNA-damaging agents as mms22D, albeit at higher doses, and are not hypersensitive to IR or UV (Verkade et al 1999;Sheedy et al 2005; our own observations). Cells disrupted for both mms22 and brc1 showed a moderate synergistic growth defect compared to mms22D alone ( Figure 7B), suggesting that the two proteins do not function exclusively together.…”

“…Brc1 is thought to function primarily in S-phase where it aids in the replication of damaged DNA (Verkade et al 1999;Sheedy et al 2005). Brc1 was initially identified as a high-copy suppressor of smc6-74 (Verkade et al 1999), which encodes a subunit of the essential ''structural maintenance of chromosomes'' Smc5/6 complex that functions in chromosome organization and DNA repair (Lehmann et al 1995;McDonald et al 2003;Harvey et al 2004;Pebernard et al 2004Pebernard et al , 2006.…”

“…Brc1 was initially identified as a high-copy suppressor of smc6-74 (Verkade et al 1999), which encodes a subunit of the essential ''structural maintenance of chromosomes'' Smc5/6 complex that functions in chromosome organization and DNA repair (Lehmann et al 1995;McDonald et al 2003;Harvey et al 2004;Pebernard et al 2004Pebernard et al , 2006. The Brc1-mediated rescue of smc6-74 is thought to proceed via a novel Rhp18-dependent mechanism, utilizing multiple nucleases to facilitate the initial cleavage of abnormal structures that arise due to compromised Smc5/6 function and their subsequent processing by HR (Sheedy et al 2005;Lee et al 2007). Loss of Brc1 function results in sensitivity to a range of DNA-damaging drugs that generate lesions specifically during S-phase or impede DNA replication (Verkade et al 1999;Sheedy et al 2005).…”

“…The Brc1-mediated rescue of smc6-74 is thought to proceed via a novel Rhp18-dependent mechanism, utilizing multiple nucleases to facilitate the initial cleavage of abnormal structures that arise due to compromised Smc5/6 function and their subsequent processing by HR (Sheedy et al 2005;Lee et al 2007). Loss of Brc1 function results in sensitivity to a range of DNA-damaging drugs that generate lesions specifically during S-phase or impede DNA replication (Verkade et al 1999;Sheedy et al 2005).…”

TORC2 Is Required to Maintain Genome Stability during S Phase in Fission Yeast

“…Additionally, TORC2-Gad8 mutant cells are insensitive to IR. The resistance of TORC2-Gad8 mutant cells to transient exposure to replicative stress is in contrast to the sensitivity of HR mutants, such as rad52 and rad51, to such conditions (67). Moreover, following a transient CPT treatment, which markedly elevates the number of Rad52 foci, we detected no major defects in returning to basal Rad52 foci levels in ⌬tor1 or ⌬gad8 mutant cells (Fig.…”