Control of cell growth and division is essential to prevent aberrant cellular development but the biochemical mechanisms involved are still poorly understood. In July Nature Cell Biology, Duncan Clarke and colleagues from the Scripps Research Institute, La Jolla, California identified the protein securin Pds1p as vital in determining the continuation of cell division.

Using the budding yeast as a model, Clarke et al. showed that the coupling of the completion of genome replication with mitosis relies on the regulation of Pds1p levels. In addition, Mec1p is needed to maintain Pds1p levels under S-phase checkpoint conditions. But kinase Rad53p and the DNA-damage checkpoint kinase Chk1p are dispensable for this response (Nat Cell Biol 2001, 3:619-626).

Thus, the Pds1p-dependent late-S-phase checkpoint pathway couples replication with mitosis but is mechanistically distinct from the G2 DNA-damage checkpoint. This mechanism could be a new target for therapy to guard against genome...