Cohesin (red) keeps centromeres together.
Peters/AAAS
Cohesin was a long sought-after protein complex: a glue for sister chromatids that is dissolved at the onset of anaphase thanks to cleavage of its SCC1 subunit by the protease separase. In budding yeast, cohesin lived up to its billing as a complex that was destroyed at anaphase onset.
But in humans cells its behavior was less convincing. The vast majority of cohesin comes off human chromosomes in prophase and prometaphase, coincident with the dissociation of sister chromatid arms. Only after a hard look is it apparent that a little cohesin is left at the centromere. Now Jan-Michael Peters and colleagues (Research Institute of Molecular Pathology (IMP), Vienna, Austria) have used a noncleavable SCC1 to show that cleavage of this residual SCC1 is indeed required for correct chromosome segregation and cytokinesis.
“Because so little SCC1 is cleaved in human...
