COHESINS - CHROMOSOMAL-PROTEINS THAT PREVENT PREMATURE SEPARATION OF SISTER CHROMATIDS

Cohesion between sister chromatids opposes the splitting force exerted by microtubules, and loss of this cohesion is responsible for the sub sequent separation of sister chromatids during anaphase. We describe t hree chromosmal proteins that prevent premature separation of sister c hromatids in yeast. Two, Smc1p and Smc3p, are members of the SMC famil y, which are putative ATPases with coiled-coil domains. A third protei n, which we call Scc1p, binds to chromosomes during S phase, dissociat es from them at the metaphase-to-anaphase transition, and is degraded by the anaphase promoting complex. Association of Scc1p with chromatin depends on Smc1p. Proteins homologous to Scclp exist in a variety of eukaryotic organisms including humans. A common cohesion apparatus mig ht be used by all eukaryotic cells during both mitosis and meiosis.