Abstract
PCNA sliding clamp binds factors through which histone deposition, chromatin remodeling, and DNA repair are coupled to DNA replication. PCNA also directly binds Eco1/Ctf7 acetyltransferase, which in turn activates cohesins and establishes cohesion between nascent sister chromatids. While increased recruitment thus explains the mechanism through which elevated levels of chromatin-bound PCNA rescue eco1 mutant cell growth, the mechanism through which PCNA instead worsens cohesin mutant cell growth remains unknown. Possibilities include that elevated levels of long-lived chromatin-bound PCNA reduce either cohesin deposition onto DNA or cohesin acetylation. Instead, our results reveal that PCNA increases the levels of both chromatin-bound cohesin and cohesin acetylation. Beyond sister chromatid cohesion, PCNA also plays a critical role in genomic stability such that high levels of chromatin-bound PCNA elevate genotoxic sensitivities and recombination rates. At a relatively modest increase of chromatin-bound PCNA, however, fork stability and progression appear normal in wildtype cells. Our results reveal that even a moderate increase of PCNA indeed sensitizes cohesin mutant cells to DNA damaging agents and in a process that involves the DNA damage response kinase Mec1(ATR), but not Tel1(ATM). These and other findings suggest that PCNA mis-regulation results in genome instabilities that normally are resolved by cohesin. Elevating levels of chromatin-bound PCNA may thus help target cohesinopathic cells linked that are linked to cancer.
Highlights
During S phase, the cellular genome duplicates and each sister chromatid becomes tethered together to ensure proper inheritance of the genome during mitosis
Elevated levels of chromatin-bound PCNA instead exacerbates the growth defects of the cohesin subunits [15, 33], a surprising phenotype given that the cohesin subunit Smc3 is the target of Eco1 acetylation [12, 13, 102]
ELG1 deletion is mutagenic and may have adverse impacts beyond PCNA unloading while moderate increases in PCNA appear fully tolerated by wildtype cells [58, 60, 63, 73, 75, 103]
Summary
During S phase, the cellular genome duplicates and each sister chromatid becomes tethered together to ensure proper inheritance of the genome during mitosis. Sister chromatid tethering is maintained by cohesin, a complex comprised of Smc, Smc, and Mcd1/Scc1/RAD21 along with auxiliary subunits Pds, Scc3/Irr, Rad61/WAPL and, in vertebrate cells, Sororin [1,2,3,4,5,6,7]. Cohesin deposition onto DNA requires the cohesin loader, comprised of Scc and Scc, which functions through a large part of the cell cycle but is essential during S phase for cohesins to participate in sister chromatin tethering [8, 9]. Deposition onto chromatin, is not sufficient for cohesion. Eco1/Ctf ( Eco1) is an acetyltransferase that converts.
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