Splitting the Chromosome: Cutting the Ties That Bind Sister Chromatids

In eukaryotic cells, sister DNA molecules remain physically connected from their production at S phase until their separation during anaphase. This cohesion is essential for the separation of sister chromatids to opposite poles of the cell at mitosis. It also permits chromosome segre-gation to take place long after duplication has been completed. Recent work has identiÞed a multisubunit complex called cohesin that is essential for connecting sisters. Proteolytic cleavage of one of cohesinÕs subunits may trigger sister separation at the onset of anaphase. Back to Basics: Chromosome Mechanics Instructions for the behavior of every cell in the bodies of worms, flies, and humans will soon reside in public databases for all to read. A complete set of such instructions, packaged as chromosomes, is inherited b