Importance of Polη for Damage-Induced Cohesion Reveals Differential Regulation of Cohesion Establishment at the Break Site and Genome-Wide

摘要

Genome integrity depends on correct chromosome segregation, which in turn relies on cohesion between sister chromatids from S phase until anaphase. S phase cohesion, together with DNA double-strand break (DSB) recruitment of cohesin and formation of damage-induced (DI) cohesion, has previously been shown to be required also for efficient postreplicative DSB repair. The budding yeast acetyltransferase Eco1 (Ctf7) is a common essential factor for S phase and DI-cohesion. The fission yeast Eco1 ortholog, Eso1, is expressed as a fusion protein with the translesion synthesis (TLS) polymerase Polη. The involvement of Eso1 in S phase cohesion was attributed to the Eco1 homologous part of the protein and bypass of UV-induced DNA lesions to the Polη part. Here we describe an additional novel function for budding yeast Polη, i.e. formation of postreplicative DI genome-wide cohesion. This is a unique Polη function not shared with other TLS polymerases. However, Polη deficient cells are DSB repair competent, as Polη is not required for cohesion locally at the DSB. This reveals differential regulation of DSB–proximal cohesion and DI genome-wide cohesion, and challenges the importance of the latter for DSB repair. Intriguingly, we found that specific inactivation of DI genome-wide cohesion increases chromosomal mis-segregation at the entrance of the next cell cycle, suggesting that S phase cohesion is not sufficient for correct chromosome segregation in the presence of DNA damage. Author Summary Correct chromosome segregation requires that sister chromatids are held together by the protein complex cohesin, from S phase until anaphase. This S phase established cohesion is, together with DSB recruitment of cohesin and formation of damage-induced (DI) cohesion, also important for repair of DSBs. Eco1 is a common essential factor for S phase and DI-cohesion. The fission yeast Eco1 ortholog, Eso1, is important both for S phase cohesion and for bypass of UV-induced lesions, and is expressed as a fusion protein with Polη. The cohesion function has been attributed solely to Eso1 and the lesion bypass function to the Polη part of the protein. As we found the interaction between the two proteins intriguing, we decided to look for a functional connection also in budding yeast. Indeed, despite being dispensable for S phase cohesion, budding yeast Polη is required for formation of DI genome-wide cohesion. However, Polη-deficient cells are DSB repair competent, revealing differential regulation of DI-cohesion at the break and genome-wide. This finding challenges the importance of DI genome-wide cohesion for DSB repair, and based on our findings we suggest that S phase cohesion is not sufficient for correct chromosome segregation in the presence of DNA damage.