Roles of the Mitotic Inhibitors Wee1 and Mik1 in the G₂ DNA Damage and Replication Checkpoints

Abstract

The G₂ DNA damage and DNA replication checkpoints in many organisms act through the inhibitory phosphorylation of Cdc2 on tyrosine-15. This phosphorylation is catalyzed by the Wee1/Mik1 family of kinases. However, the in vivo role of these kinases in checkpoint regulation has been unclear. We show that, in the fission yeastSchizosaccharomyces pombe, Mik1 is a target of both checkpoints and that the regulation of Mik1 is, on its own, sufficient to delay mitosis in response to the checkpoints. Mik1 appears to have two roles in the DNA damage checkpoint; one in the establishment of the checkpoint and another in its maintenance. In contrast, Wee1 does not appear to be involved in the establishment of either checkpoint.

ACKNOWLEDGMENTS

We are grateful to Kathy Gould for providing the nmt1:PTPase construct with which preliminary experiments were done, Michael Boddy for providing the glutathione S-transferase Wee1, and Beth Baber-Furnari for providing the chk1⁺:9Myc strain. We also thank the members of the TSRI Cell Cycle Group for many interesting discussions and useful suggestions, in particular Jean-Marc Brondello for suggesting the use of a conditional mik1allele.

N.R. was supported by an NIH postdoctoral fellowship and a special fellowship from the Leukemia and Lymphoma Society. This work was supported by an NIH grant awarded to P.R.