Cohesin's binding to chromosomes depends on a separate complex consisting of Scc2 and Scc4 proteins

Cohesion between sister chromatids depends on a multisubunit cohesin comple x that binds to chromosomes around DNA replication and dissociates from the m at the onset of anaphase. Scc2p, though not a cohesin subunit, is also re quired for sister chromatid cohesion. We show here that Scc2p forms a compl ex with a novel protein, Scc4p, which is also necessary for sister cohesion . In scc2 or scc4 mutants, cohesin complexes form normally but fail to bind both to centromeres and to chromosome arms. Our data suggest that a major role for the Scc2p/Scc4p complex is to facilitate the loading of cohesin co mplexes onto chromosomes.