Cohesin Ubiquitylation and Mobilization Facilitate Stalled Replication Fork Dynamics

Abstract

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 Rsp5 ubiquitin ligase in promoting survival to replication stress by preserving stalled fork integrity. Rsp5 physically interacts with cohesin and the Mec1 kinase, thus promoting checkpoint-dependent cohesin ubiquitylation and cohesin-mediated fork protection. Ubiquitylation mediated by Rsp5 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 Rsp5 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.

Error‐free DNA damage tolerance pathway is facilitated by the Irc5 translocase through cohesin

“…Disruption of IRC5 resulted in decreased levels of chromatin‐bound cohesin at centromeres, chromosome arms, and rDNA suggesting that Irc5 contributes to cohesin loading onto chromatin throughout the genome (Litwin et al , ). Moreover, it has been recently shown that cohesin complexes accumulate near stalled replication forks and support formation of SCJs in the context of DDT (Tittel‐Elmer et al , ; Fumasoni et al , ; Frattini et al , ). Taking these results into account, we decided to determine whether Irc5 facilitates DDT through cohesin loading during replication stress.…”

“…This confirms that Scc2/Scc4 activity is crucial for cohesin association with chromatin at sites of replication arrest. Previous reports showed that lack of functional cohesin results in decreased survival, defects in replication completion, accumulation of ssDNA gaps, and strong reduction or lack of SCJ formation (Tittel‐Elmer et al , ; Fumasoni et al , ; Frattini et al , ). These results suggest that the cohesin loader and cohesin function in a common pathway with Rad18‐mediated TS during MMS‐induced replication stress.…”

Replisome‐Cohesin Interfacing: A Molecular Perspective

“…Recent evidence in yeast cells has suggested that the p97/Cdc48 ubiquitin selective segregase remodels cohesin complexes to promote their removal from unreplicated chromatin upon engagement by replication forks . Mutants impairing the function of Cdc48 or the Rsp5 Bul2 ubiquitin ligase show increased binding of cohesin close to replication forks but reduced association to nascent DNA, suggesting that cohesin ubiquitylation and remodeling by Cdc48 are required for its mobilization and translocation to nascent duplexes behind forks (Figure c).…”

“…This option, in which cohesin and replisome factors may not happen to interact, fails to explain how cohesion establishment is achieved, as cohesin ring locking would still need to be coordinated with the fork‐associated Eco1 locking function. In addition, recent studies suggest that cohesin molecules already bound to unreplicated chromatin are utilized to establish cohesion upon fork passage . A simple solution to couple sister chromatid entrapment and cohesin locking is provided by models in which the replisome “replicates through” cohesin molecules encircling parental DNA (Figure b).…”

“…Establishment of sister chromatid cohesion is intimately intertwined with chromosome duplication and is mediated by factors progressing with replication machineries . On the other hand, recent studies have linked cohesin function to the structural organization and stability of replication forks, particularly important in the presence of DNA damage or replicative stress . Hence, interfacing between cohesin and replication forks has emerged as a central event potentially impacting on chromosome metabolism, transmission, and integrity.…”