Cohesins , the proteins that are thought to anchor sister chromatids to one another before anaphase, must be present during DNA replication if cohesion is to be established. In the 4 August Science Wang et al . provide a possible link between replication and cohesion (Science 2000, 289 :774-779). They describe an essential DNA polymerase in budding yeast that both has polymerase activity and is required for sister chromatid cohesion. They suggest that the replication fork may switch to this polymerase at special cohesion sites, where the polymerase then recruits cohesins.