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Roles of the mitotic inhibitors Wee1 and Mik1 in the G(2) DNA damage and replication checkpoints
1Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
Abstract:
The G(2) 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 yeast Schizosaccharomyces 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.
Insights
The fission yeast Mik1 kinase is regulated by DNA damage and replication checkpoints, delaying mitosis. Mik1 plays dual roles in DNA damage checkpoint establishment and maintenance.
Area of Science:
- Cellular biology
- Molecular genetics
- Yeast genetics
Background:
- The G(2) DNA damage and replication checkpoints regulate cell cycle progression by inhibiting Cdc2 kinase via phosphorylation at tyrosine-15.
- Wee1/Mik1 kinases catalyze this inhibitory phosphorylation, but their precise in vivo roles in checkpoint control remain incompletely understood.
Purpose of the Study:
- To elucidate the in vivo function of Wee1 and Mik1 kinases in checkpoint-mediated mitotic delay in the fission yeast Schizosaccharomyces pombe.
Main Methods:
- Investigated the role of Mik1 as a target of G(2) checkpoints.
- Assessed the sufficiency of Mik1 regulation in delaying mitosis.
- Differentiated the roles of Mik1 and Wee1 in checkpoint establishment and maintenance.
Main Results:
- Demonstrated that Mik1 is a direct target of both DNA damage and replication checkpoints in S. pombe.
- Showed that Mik1 regulation alone is sufficient to induce a mitotic delay in response to checkpoint activation.
- Identified two distinct roles for Mik1 in the DNA damage checkpoint: checkpoint establishment and maintenance.
- Found that Wee1 kinase is not involved in the initial establishment of either checkpoint.
Conclusions:
- Mik1 kinase is a key regulator of mitotic entry downstream of the G(2) checkpoints in fission yeast.
- Mik1's dual roles in checkpoint establishment and maintenance highlight its critical importance in DNA damage response.
- Wee1's lack of involvement in checkpoint establishment suggests a specialized role, distinct from Mik1, in cell cycle control.