Sororin is a positive regulator of sister chromatid cohesion that interacts with 
the cohesin complex. Sororin is required for the increased stability of the 
cohesin complex on chromatin following DNA replication and sister chromatid 
cohesion during G(2). The mechanism by which sororin ensures cohesion is 
currently unknown. Because the primary sequence of sororin does not contain any 
previously characterized structural or functional motifs, we have undertaken a 
structure-function analysis of the sororin protein. Using a series of mutant 
derivatives of sororin, we show that the ability of sororin to bind to chromatin 
is separable from both its role in sister chromatid cohesion and its interaction 
with the cohesin complex. We also show that derivatives of sororin with 
deletions or mutations in the conserved C terminus fail to rescue the 
loss-of-cohesion phenotype caused by sororin RNAi and that these mutations also 
abrogate the association of sororin with the cohesin complex. Our data suggest 
that the interaction of the highly conserved motif at the C terminus of sororin 
with the cohesin complex is critical to its ability to mediate sister chromatid 
cohesion.