Fission yeast Srr1 and Skb1 promote isochromosome formation at the centromere

Abstract

Rad51 maintains genome integrity, whereas Rad52 causes non-canonical homologous recombination leading to gross chromosomal rearrangements (GCRs). Here we find that fission yeast Srr1/Ber1 and Skb1/PRMT5 promote GCRs at centromeres. Genetic and physical analyses show that srr1 and skb1 mutations reduce isochromosome formation mediated by centromere inverted repeats. srr1 increases DNA damage sensitivity in rad51 cells but does not abolish checkpoint response, suggesting that Srr1 promotes Rad51-independent DNA repair. srr1 and rad52 additively, while skb1 and rad52 epistatically reduce GCRs. Unlike srr1 or rad52, skb1 does not increase damage sensitivity. Skb1 regulates cell morphology and cell cycle with Slf1 and Pom1, respectively, but neither Slf1 nor Pom1 causes GCRs. Mutating conserved residues in the arginine methyltransferase domain of Skb1 greatly reduces GCRs. These results suggest that, through arginine methylation, Skb1 forms aberrant DNA structures leading to Rad52-dependent GCRs. This study has uncovered roles for Srr1 and Skb1 in GCRs at centromeres.

Gross Chromosomal Rearrangement at Centromeres

“…Finding Skb1 RMTase targets is vital to elucidate how Skb1 causes isochromosome formation. Remarkably, skb1 and srr1 deletions additively reduce GCR rates [136], showing that Skb1 and Srr1 have nonoverlapping roles in GCR. In contrast to skb1, a srr1 mutation further reduces GCR rates in rad52-R45K mutant cells, suggesting a role of Srr1 in the Rad52-independent GCR pathway.…”

“…Recently, it has been shown that Skb1/PRMT5 arginine methyltransferase (RMTase) and Srr1 play roles in isochromosome formation in the absence of Rad51 [136]. Mutation in the RMTase domain of Skb1 reduces GCR rates in rad51 deletion cells [136], showing that Skb1 causes isochromosome formation through RMTase activity. Skb1 regulates cell morphology and cell cycle progression, respectively, with Slf1 and Pom1 [192][193][194][195].…”

“…In contrast to skb1, a srr1 mutation further reduces GCR rates in rad52-R45K mutant cells, suggesting a role of Srr1 in the Rad52-independent GCR pathway. srr1 and rad51 mutations synergistically increase sensitivity to DNA-damaging agents, including methyl methanesulfonate, camptothecin, and hydroxyurea [136], suggesting a role of Srr1 in Rad51-independent DNA damage repair. However, how Srr1 acts in DNA damage tolerance and causes isochromosome formation remains unknown.…”