Cohesin complex acts in the formation and maintenance of sister chromatid 
cohesion during and after S phase. Budding yeast Scc1p/Mcd1p, an essential 
subunit, is cleaved and dissociates from chromosomes in anaphase, leading to 
sister chromatid separation. Most cohesin in higher eukaryotes, in contrast, is 
dissociated from chromosomes well before anaphase. The universal role of cohesin 
during anaphase thus remains to be determined. We report here initial 
characterization of four putative cohesin subunits, Psm1, Psm3, Rad21, and Psc3, 
in fission yeast. They are essential for sister chromatid cohesion. 
Immunoprecipitation demonstrates stable complex formation of Rad21 with Psm1 and 
Psm3 but not with Psc3. Chromatin immunoprecipitation shows that cohesin 
subunits are enriched in broad centromere regions and that the level of 
centromere-associated Rad21 did not change from metaphase to anaphase, very 
different from budding yeast. In contrast, Rad21 containing similar cleavage 
sites to those of Scc1p/Mcd1p is cleaved specifically in anaphase. This cleavage 
is essential, although the amount of cleaved product is very small (<5%). Mis4, 
another sister chromatid cohesion protein, plays an essential role for loading 
Rad21 on chromatin. A simple model is presented to explain the specific behavior 
of fission yeast cohesin and why only a tiny fraction of Rad21 is sufficient to 
be cleaved for normal anaphase.