Cohesin regulation: fashionable ways to wear a ring

Cohesin is a multiprotein complex, conserved from yeast to humans, that mediates sister chromatid cohesion. Its ring-shaped structure first suggested that it may perform its task by embracing the sister chromatids. The interaction of cohesin with chromatin is tightly regulated throughout the cell cycle, and several proteins contribute to cohesin loading and mobilization along DNA, establishment of cohesin-mediated cohesion, and removal of cohesin during mitosis. Recent studies suggest that distinct cohesin populations exist in different chromosomal regions and have particular requirements in their dynamic interaction with chromatin. In this review, I briefly summarize these studies and discuss their implications for current and future models of cohesin behavior.