Biochemical reconstitution of sister chromatid cohesion establishment during DNA replication

SUMMARY Concomitant with DNA replication, the ring-shaped cohesin complex encircles both newly synthesized sister chromatids, enabling their faithful segregation during cell divisions. Our molecular understanding of how cohesin co-entraps both replication products remains incomplete. Here, we reconstitute sister chromatid cohesion establishment using purified budding yeast proteins. Cohesin rings, initially loaded onto template DNA, remain DNA-bound during DNA synthesis and encircle both replication products. Additionally, DNA replication instigates new cohesin recruitment, as a second pathway that generates sister chromatid cohesion. In both scenarios, cohesin often embraces only one of the two replication products, suggestive of a two-step sister chromatid capture mechanism. Sister chromatid co-entrapment occurs independently of replication fork-associated cohesion establishment factors, suggesting a role for the latter during chromatin replication or in facilitating the subsequent cohesin acetylation reaction. Our results make sister chromatid cohesion establishment amenable to direct experimental exploration.