How and When the Genome Sticks Together

摘要

Before a eukaryotic cell divides, it generates a copy of its genome by DNA replication. As a result, each chromo-some in a postreplicative cell contains two identical DNA molecules, the sister chro-matids. These DNA molecules are physically connected to each other, a phenomenon known as sister-chromatid cohesion. Cohesion is essential for the symmetrical segregation of chromosomes during cell division. Not surprisingly, cohesion is normally established when sister chromatids are synthesized during S phase of the cell division cycle (see the figure). But cohesion also helps to repair damaged DNA after S phase has been completed. Two papers in this issue, by Stroem et al. (3) on page 242 and Uenal et al. (4) on page 245, show that cohesion can be established in response to DNA damage independently of DNA replication. This overturns a long-held belief that cohesion is strictly coupled to DNA synthesis. The papers also imply that DNA damage may have a broader impact than previously thought, triggering genome-wide protection of chromosome integrity.