Cohesin Ubiquitylation and Mobilization Facilitate Stalled Replication Fork Dynamics

Replication fork integrity is challenged in conditions of stress and protected by the Mec1/ATR checkpoint to preserve genome stability. Still poorly understood in fork protection is the role played by the structural maintenance of chromosomes (SMC) cohesin complex. We uncovered a role for the Rsp5Bul2 ubiquitin ligase in promoting survival to replication stress by preserving stalled fork integrity. Rsp5Bul2 physically interacts with cohesin and the Mec1 kinase, thus promoting checkpoint-dependent cohesin ubiquitylation and cohesin-mediated fork protection. Ubiquitylation mediated by Rsp5Bul2 promotes cohesin mobilization from chromatin neighboring stalled forks, likely by stimulating the Cdc48/p97 ubiquitin-selective segregase, and its timely association to nascent chromatids. This Rsp5Bul2 fork protection mechanism requires the Wpl1 cohesin mobilizer as well as the function of the Eco1 acetyltransferase securing sister chromatid entrapment. Our data indicate that ubiquitylation facilitates cohesin dynamic interfacing with replication forks within a mechanism preserving stalled-fork functional architecture. [Display omitted] •Rsp5Bul2 modulates cohesin function to stabilize stalled replication forks•Cohesin is ubiquitylated in an Rsp5Bul2- and Mec1(ATR)-dependent manner•Rsp5Bul2 and Cdc48 mediate cohesin translocation to nascent chromatids•Nascent chromatid entrapment by cohesin promotes fork integrity Frattini et al. uncover a mechanism that mediates the interfacing of replication forks with chromatin-bound cohesin complexes. Coordination between factors that promote cohesin ubiquitylation, mobilization from chromatin, and entrapment of nascent chromatids are essential to stabilize replication forks experiencing stress.