FISSION YEAST WEE1 PROTEIN-KINASE IS NOT REQUIRED FOR DNA DAMAGE-DEPENDENT MITOTIC ARREST

CHECKPOINTS maintain the dependency relationships between discrete eve nts in the cell cycle (for example, ensuring mitosis does not occur be fore DNA replication is complete)1,2. In Schizosaccharomyces pombe, mi totic checkpoints monitor DNA synthesis3 and the presence of DNA damag e4,5. The replication-dependent mitotic checkpoint prevents mitosis by inactivating p34cdc2 kinase3. The mechanism by which the DNA damage c heckpoint interacts with the mitotic machinery is distinct from that u sed by the replication checkpoint4,5. The activity of p34cdc is contro lled, in part, by the wee 1 protein kinase6, which inactivates cdc2 th rough phosphorylation at tyrosine-15 (ref. 7). Here we report normal m itotic arrest after DNA damage in S. pombe cells in which the wee 1 ge ne is defective or missing. We suggest why these findings contradict a recent report8 which suggested that the wee1 gene product was require d for DNA damage-dependent mitotic arrest.