Sister chromatid cohesion is mediated by individual cohesin complexes

• DOI: 10.1126/science.adl4606
• Publication Date: 2024-03-07T18:59:04Z
• Authors: Fena Ochs; Charlotte Green; Aleksander Tomasz...; Lior Pytowski; Sofia Kolesnikova; Jill Brown; Daniel Wolfram Ge...; Veronica Buckle; Lothar Schermelleh; Kim Ashley Nasmyth
• Keywords: 0303 health sciences; 03 medical and health sciences; Chromosomal Proteins, Non-Histone; Humans; Cell Cycle Proteins; DNA; Chromatids; Cohesins; Chromatin

Eukaryotic genomes are organized by loop extrusion and sister chromatid cohesion, both mediated by the multimeric cohesin protein complex. Understanding how cohesin holds sister DNAs together, and how loss of cohesion causes age-related infertility in females, requires knowledge as to cohesin’s stoichiometry in vivo. Using quantitative super-resolution imaging, we identified two discrete populations of chromatin-bound cohesin in postreplicative human cells. Whereas most complexes appear dimeric, cohesin that localized to sites of sister chromatid cohesion and associated with sororin was exclusively monomeric. The monomeric stoichiometry of sororin:cohesin complexes demonstrates that sister chromatid cohesion is conferred by individual cohesin rings, a key prediction of the proposal that cohesion arises from the co-entrapment of sister DNAs.