Cohesin sumoylation is required for repression of subtelomeric gene expression in Saccharomyces cerevisiae

Cohesin, first described for its role in sister chromatid cohesion, impacts several chromosomal processes, some of which (chromosome segregation, replication and repair) are regulated by its post-translational modifications. Previously, we reported a silent information regulator (SIR) complex-independent role for cohesin in subtelomeric gene silencing. Here, we investigated the requirement of cohesin sumoylation in subtelomeric repression. We created sumoylation-deficient cohesin by fusing the catalytic domain of a SUMO protease, ULP1, to the C-terminus of the cohesin subunit Mcd1 (also known as Scc1) to create Mcd1-UD. We show that cohesin sumoylation is required for repression of sub-telomeric genes. Consistent with a SIR-independent role of cohesin in telomere silencing, SIR proteins remained bound to a de-repressed subtelomeric gene in MCD1-UD-expressing cells, and subtelomeric gene expression further increased upon SIR2 deletion. Telomere cohesion was unaltered in this mutant, suggesting that telomere cohesion and regulation of sub-telomere gene silencing are separable functions of cohesin. Telomere tethering to the nuclear envelope and telomere compaction are defective in MCD1-UD cells, indicating that sumoylation contributes to the role of cohesin in subtelomeric chromosome organization. Our results establish the relevance of cohesin sumoylation in repression of subtelomeric gene expression and organization of subtelomeric chromatin.