Separating sister chromatids

Loss of cohesion between sister chromatids triggers their segregation durin g anaphase. Recent work has identified both a cohesin complex that holds si sters together and a sister-separating protein, separin, that destroys cohe sion. Separins are bound by inhibitory proteins whose proteolysis at the me taphase-anaphase transition is mediated by the anaphase-promoting complex a nd its activator protein CDC20 (APC(CDC20)). When chromosomes are misaligne d, a surveillance mechanism (checkpoint) blocks sister separation by inhibi ting APC(CDC20). Defects in this apparatus are implicated in causing aneupl oidy in human cells.