cdc25 is a specific tyrosine phosphatase that directly activates p34cdc2
J Gautier1, M J Solomon, R N Booher
1Department of Biochemistry and Biophysics, University of California, San Francisco 94143-0448.
Cell
|October 4, 1991
Summary
The CDC25 protein phosphatase specifically dephosphorylates p34cdc2 on tyrosine, activating the cyclin-p34cdc2 complex and initiating M phase in Xenopus oocytes.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- The cell cycle is regulated by protein kinases and phosphatases.
- CDC25 is a key regulator of the cell cycle, controlling the activity of the cyclin-p34cdc2 complex.
- The precise mechanism of CDC25's phosphatase activity and substrate specificity has been under investigation.
Purpose of the Study:
- To investigate the enzymatic activity and substrate specificity of the CDC25 protein.
- To determine if CDC25 directly dephosphorylates p34cdc2 and regulates M phase entry.
- To characterize the role of CDC25 in controlling the phosphorylation state of p34cdc2.
Main Methods:
- Expression of Drosophila CDC25 in bacterial and yeast systems.
- In vitro phosphatase assays using bacterially expressed p34cdc2.
- Analysis of M phase induction in Xenopus oocytes and egg extracts.
- Site-directed mutagenesis of the putative catalytic site of CDC25.
Main Results:
- Drosophila CDC25 activates inactive cyclin-p34cdc2 and induces M phase in Xenopus oocytes.
- CDC25 exhibits sequence homology to protein tyrosine phosphatases.
- Bacterially expressed CDC25 specifically dephosphorylates p34cdc2 on Tyr-15 in vitro.
- Mutations in the catalytic site abolish both in vitro and in vivo CDC25 activity.
- CDC25 demonstrates high specificity for p34cdc2, with minimal dephosphorylation of other tyrosine-phosphorylated proteins.
Conclusions:
- CDC25 is a specific protein tyrosine phosphatase that directly dephosphorylates p34cdc2 on Tyr-15.
- This dephosphorylation event is critical for the activation of the cyclin-p34cdc2 complex and the initiation of M phase.
- CDC25 plays a crucial role in regulating MPF (maturation-promoting factor) activation through specific dephosphorylation of p34cdc2.
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