Cohesin in space and time: architecture and oligomerization in vivo.

Cohesin helps mediate sister chromatid cohesion, chromosome condensation, DNA repair and transcription regulation. Cohesin can tether two regions of DNA and also extrude DNA loops. We interrogated cohesin architecture, oligomerization and function in vivo through proximity based labeling of cohesin domains. Our results suggest that the hinge and head domain of cohesin both bind DNA, and that cohesin coiled coils bend, bringing the head and hinge together to form a butterfly conformation. Our data also suggest that cohesin efficiently oligomerizes on and off DNA. The levels of oligomers and their distribution on chromosomes are cell cycle regulated. Cohesin oligomerization is blocked by mutations in distinct domains of the Smc3p and Mcd1p subunits of cohesin or in Pds5p, a cohesin regulator. These mutations also block the maintenance of cohesion but not loop extrusion, suggesting that cohesin oligomerization plays a specific role in the maintenance of cohesion.