Sister chromatid cohesion is crucial for chromosome segregation during mitosis. 
Loss of cohesion very possibly triggers sister separation at the metaphase --> 
anaphase transition. This process depends on the destruction of anaphase 
inhibitory proteins like Pds1p (Cut2p), which is thought to liberate a 
sister-separating protein Esp1p (Cut1p). By looking for mutants that separate 
sister centromeres in the presence of Pds1p, this and a previous study have 
identified six proteins essential for establishing or maintaining sister 
chromatid cohesion. Four of these proteins, Scc1p, Scc3p, Smc1p, and Smc3p, are 
subunits of a 'Cohesin' complex that binds chromosomes from late G1 until the 
onset of anaphase. The fifth protein, Scc2p, is not a stoichiometric Cohesin 
subunit but it is required for Cohesin's association with chromosomes. The sixth 
protein, Eco1p(Ctf7p), is not a Cohesin subunit. It is necessary for the 
establishment of cohesion during DNA replication but not for its maintenance 
during G2 and M phases.