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

Abstract

DNA damage tolerance (DDT) mechanisms facilitate replication resumption and completion when DNA replication is blocked by bulky DNA lesions. In budding yeast, template switching (TS) via the Rad18/Rad5 pathway is a favored DDT pathway that involves usage of the sister chromatid as a template to bypass DNA lesions in an error-free recombination-like process. Here, we establish that the Snf2 family translocase Irc5 is a novel factor that promotes TS and averts single-stranded DNA persistence during replication. We demonstrate that, during replication stress, Irc5 enables replication progression by assisting enrichment of cohesin complexes, recruited in an Scc2/Scc4-dependent fashion, near blocked replication forks. This allows efficient formation of sister chromatid junctions that are crucial for error-free DNA lesion bypass. Our results support the notion of a key role of cohesin in the completion of DNA synthesis under replication stress and reveal that the Rad18/Rad5-mediated DDT pathway is linked to cohesin enrichment at sites of perturbed replication via the Snf2 family translocase Irc5.

The Emerging Role of Cohesin in the DNA Damage Response

“…However, neither Mec1 and Tel1 kinases nor H2A phosphorylation was required for cohesin binding to HU-arrested replication forks. In fact, only the mec1 Δ tel1 Δ double deletion led to a significant decrease of cohesin levels on chromatin [47,191]. This suggests that molecular requirements for cohesin accumulation at stalled replication forks may differ from the mechanisms determined for DSB-induced cohesin recruitment.…”

“…In the absence of IRC5 , the cohesin complexes accumulate more slowly and to a lesser extent at early replication origins during MMS treatment. These data may point to an important role of chromatin structure in replication stress-induced cohesin enrichment at replication sites [191]. It was also shown that in response to HU treatment, Smc1, Smc3, and Scc1 cohesin subunits are ubiquitylated by the Rsp5 Bul2 ubiquitin ligase (NEDD4 in humans) in a Mec1-dependent manner [192].…”

“…It has been shown that the cohesin loader and cohesin are crucial for survival in the presence of a wide range of genotoxins [190,191,193,194,196,197]. Moreover, while reduction of cohesin levels to 13% of wild type levels has no effect on sister chromatid cohesion, it leads to increased sensitivity to DNA damaging agents [198].…”

“…Genetic analysis revealed that during MMS-induced replication stress cohesin work in a common pathway with Rad18-mediated TS but independently of TLS or HR ([191] and data to be submitted for publication). In agreement with these data, it was shown that during MMS treatment, cohesin accumulates near stalled replication forks to promote efficient formation of X-shaped molecules that are crucial for TS.…”

PRDM9 activity depends on HELLS and promotes local 5-hydroxymethylcytosine enrichment

“…HELLS implication in genome integrity has also been detected in Neurospora crassa ( Basenko et al, 2016 ) and Saccharomyces cerevisiae ( Litwin et al, 2017 ). In S. cerevisiae , the HELLS orthologue Irc5 is required for DNA damage tolerance, and this function implies the loading of the cohesin complex at replication forks ( Litwin et al, 2018 ). In S. cerevisiae , cohesin recruitment facilitates DSB repair ( Ström et al, 2004 ; Unal et al, 2004 ).…”