Schizosaccharomyces pombe DNA translocases Rrp1 and Rrp2 have distinct roles at centromeres and telomeres that ensure genome stability

Replication stress response in fission yeast differentially depends on maintaining proper levels of Srs2 helicase and Rrp1, Rrp2 DNA translocases

Homologous recombination is a key process that governs the stability of eukaryotic genomes during DNA replication and repair. Multiple auxiliary factors regulate the choice of homologous recombination pathway in response to different types of replication stress. Using Schizosaccharomyces pombe we have previously suggested the role of DNA translocases Rrp1 and Rrp2, together with Srs2 helicase, in the common synthesis-dependent strand annealing sub-pathway of homologous recombination. Here we show that all three proteins are important for completion of replication after hydroxyurea exposure and provide data comparing the effect of overproduction of Srs2 with Rrp1 and Rrp2. We demonstrate that Srs2 localises to rDNA region and is required for proper replication of rDNA arrays. Upregulation of Srs2 protein levels leads to enhanced replication stress, chromosome instability and viability loss, as previously reported for Rrp1 and Rrp2. Interestingly, our data suggests that dysregulation of Srs2, Rrp1 and Rrp2 protein levels differentially affects checkpoint response: overproduction of Srs2 activates simultaneously DNA damage and replication stress response checkpoints, while cells overproducing Rrp1 mainly launch DNA damage checkpoint. On the other hand, upregulation of Rrp2 primarily leads to replication stress response checkpoint activation. Overall, we propose that Srs2, Rrp1 and Rrp2 have important and at least partially independent functions in the maintenance of distinct difficult to replicate regions of the genome.

Rrp1 translocase and ubiquitin ligase activities restrict the genome destabilising effects of Rad51 in fission yeast

Rad51 is the key protein in homologous recombination that plays important roles during DNA replication and repair. Auxiliary factors regulate Rad51 activity to facilitate productive recombination, and prevent inappropriate, untimely or excessive events, which could lead to genome instability. Previous genetic analyses identified a function for Rrp1 (a member of the Rad5/16-like group of SWI2/SNF2 translocases) in modulating Rad51 function, shared with the Rad51 mediator Swi5-Sfr1 and the Srs2 anti-recombinase. Here, we show that Rrp1 overproduction alleviates the toxicity associated with excessive Rad51 levels in a manner dependent on Rrp1 ATPase domain. Purified Rrp1 binds to DNA and has a DNA-dependent ATPase activity. Importantly, Rrp1 directly interacts with Rad51 and removes it from double-stranded DNA, confirming that Rrp1 is a translocase capable of modulating Rad51 function. Rrp1 affects Rad51 binding at centromeres. Additionally, we demonstrate in vivo and in vitro that Rrp1 possesses E3 ubiquitin ligase activity with Rad51 as a substrate, suggesting that Rrp1 regulates Rad51 in a multi-tiered fashion.