The cohesin complex is best known for its role in sister chromatid cohesion. 
Over the past few years, it has become apparent that cohesin also regulates gene 
expression, but the mechanisms by which it does so are unknown. Recently, three 
groups mapped numerous cohesin-binding sites in mammalian chromosomes and found 
substantial overlap with the CCCTC-binding factor (CTCF).1-3 CTCF is an 
insulator protein that blocks enhancer-promoter interactions, and the 
investigators found that cohesin also contributes to this activity. Thus, these 
studies demonstrate at least one mechanism by which cohesin can control gene 
expression.