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Human and yeast cdk-activating kinases (CAKs) display distinct substrate specificities
P Kaldis1, A A Russo, H S Chou
1Yale University School of Medicine, Department of Molecular Biophysics and Biochemistry, New Haven, Connecticut 06520-8024, USA.
Molecular Biology of the Cell
|September 3, 1998
Summary
Budding yeast Cak1p and human p40(MO15) activate cyclin-dependent kinases (cdks) differently. Cak1p targets monomeric cdks, while p40(MO15) targets cdk/cyclin complexes, with distinct inhibitor sensitivities.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Cell cycle progression relies on cyclin-dependent kinases (cdks).
- Cdk activation necessitates phosphorylation by a cdk-activating kinase (CAK).
- Human CAK (p40(MO15)/cyclin H/MAT1) is part of TFIIH, phosphorylating RNA polymerase II CTD.
Purpose of the Study:
- To investigate the substrate specificities of budding yeast Cak1p and human p40(MO15).
- To compare the mechanisms of cdk activation by Cak1p and p40(MO15).
Main Methods:
- Enzyme assays comparing Cak1p and p40(MO15) substrate preferences.
- Testing the effects of cdk inhibitors on phosphorylation by Cak1p and p40(MO15).
Main Results:
- Cak1p preferentially phosphorylates monomeric cdks; p40(MO15) preferentially phosphorylates cdk/cyclin complexes.
- p40(MO15) specifically phosphorylates cdk6/cyclin D3, while Cak1p phosphorylates monomeric cdk6 and various cdk6/cyclin complexes.
- Cdk inhibitors block p40(MO15) phosphorylation but not Cak1p phosphorylation.
Conclusions:
- Cak1p and p40(MO15) exhibit distinct substrate specificities and enzyme-substrate recognition mechanisms.
- Despite phosphorylating the same residue, the activation pathways differ significantly between yeast and human CAKs.