Fork it over: the cohesion establishment factor Ctf7p and DNA replication

To produce viable progeny, cells must identify the products of chromosome replication as sister chromatids, pair them together and then maintain this cohesion until chromosome segregation. It is well established that cohesin ring-like structures maintain sister chromatid cohesion, but the molecular mechanism by which only sisters become paired (termed establishment) is highly controversial. One of the first establishment models posited in the literature suggested that cohesin complexes associated with each sister become tethered together through an active process that is intimately coupled to progression of the DNA replication fork. A subsequent model posited that the replication fork simply passes through pre-loaded cohesin rings, entrapping within both sister chromatids. The recent findings that the establishment factor Ctf7p/Eco1p is recruited to DNA and binds both a DNA polymerase processivity factor (PCNA) and the cohesin regulator Pds5p test current models of sister chromatid pairing.