The LSH/HELLS homolog Irc5 contributes to cohesin association with chromatin in yeast

Abstract

Accurate chromosome segregation is essential for every living cell as unequal distribution of chromosomes during cell division may result in genome instability that manifests in carcinogenesis and developmental disorders. Irc5 from Saccharomyces cerevisiae is a member of the conserved Snf2 family of ATP-dependent DNA translocases and its function is poorly understood. Here, we identify Irc5 as a novel interactor of the cohesin complex. Irc5 associates with Scc1 cohesin subunit and contributes to cohesin binding to chromatin. Disruption of IRC5 decreases cohesin levels at centromeres and chromosome arms, causing premature sister chromatid separation. Moreover, reduced cohesin occupancy at the rDNA region in cells lacking IRC5 leads to the loss of rDNA repeats. We also show that the translocase activity of Irc5 is required for its function in cohesion pathway. Finally, we demonstrate that in the absence of Irc5 both the level of chromatin-bound Scc2, a member of cohesin loading complex, and physical interaction between Scc1 and Scc2 are reduced. Our results suggest that Irc5 is an auxiliary factor that is involved in cohesin association with chromatin.

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

“…We have previously shown that ATPase activity of Irc5 is required for a proper level of cohesin on chromatin and viability of the thermosensitive scc2‐4 mutant. We have also demonstrated that irc5 DAEA cells fail to complement irc5 Δ‐ 1 sensitivity to MMS (Litwin et al , ). Here, we show that ATP‐dependent translocase activity of Irc5 is also important for completion of DNA replication under MMS stress (Fig ).…”

“…We have previously shown that under normal conditions Irc5 supports Scc2/Scc4 association with chromatin and the Scc2/Scc4 interaction with Scc1. We have also revealed that viability of cells bearing scc2‐4 allele grown at semi‐permissive temperature relies on Irc5 presence (Litwin et al , ). Here, we showed that both Irc5 and cohesin loading complex promote cohesin accumulation at stalled replication forks (Figs A and B, and A and B).…”

“…The irc5 ‐Δ 1 mutant grew normally and exhibited wild‐type levels of RSC8 transcript. Interestingly, irc5 ‐Δ 1 cells showed increased sensitivity to MMS (Litwin et al , ), so we decided to investigate which aspect(s) of the replication stress response is defective in this mutant.…”

“…However, our previous work revealed that Irc5 facilitates cohesin association with chromatin under normal conditions. 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 , ).…”

“…Consequently, disruption of the ATPase subunit of the RSC complex strongly decreases the levels of chromatin‐bound Scc2 resulting in low levels of cohesin complexes associated with chromatin (Lopez‐Serra et al , ). Importantly, we have previously reported that Irc5 enables efficient association of the cohesin loading complex with chromatin, allowing productive interaction between the cohesin loader and cohesin (Litwin et al , ). How Irc5 enables Scc2/Scc4 interaction with chromatin is not yet known.…”