title: Evidence for a pre-restriction point Cdk3 activity.
abstract: We have examined the activity of cyclin-dependent kinase 3 (cdk3) during G1-phase of the cell cycle in Chinese Hamster Ovary (CHO) fibroblasts. Histone H1 kinase activity associated with anti-cdk3 immunoprecipitates peaked during a brief window of time, 2-3 h prior to the restriction point. In vitro cdk3 activity was sensitive to roscovitine, a drug previously shown to inhibit cdks 1, 2, and 5, but not cdk4 or 6. Early G1-phase activation of cdk3 was downregulated by treatment of cells with MG132, an inhibitor of the proteasome, and by the protein synthesis inhibitor cycloheximide. These results provide evidence for a pre-restriction point cdk3 activity that requires both the synthesis of a regulatory subunit and degradation of an inhibitor.
authors.affiliation: Department of Biochemistry and Molecular Biology, S.U.N.Y. Upstate Medical University, 750 East Adams Street, Syracuse, New York 13210, USA.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Keezer
authors.forename: David M
authors.initials: DM
authors.lastname: Gilbert
mesh_terms: D000818:Animals; D016466:CHO Cells / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D006224:Cricetinae; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016193:G1 Phase / Q000187:drug effects / Q000502:physiology*; D007976:Leupeptins / Q000494:pharmacology; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism; D011233:Precipitin Tests; D046988:Proteasome Endopeptidase Complex; D011494:Protein Kinases / Q000276:immunology / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011687:Purines / Q000494:pharmacology; D018741:Replication Origin / Q000187:drug effects / Q000502:physiology*; D000077546:Roscovitine
chemical_list: D004791:Enzyme Inhibitors; D007976:Leupeptins; D009097:Multienzyme Complexes; D011500:Protein Synthesis Inhibitors; D011687:Purines; D000077546:Roscovitine; D003513:Cycloheximide; D011494:Protein Kinases; C102333:histone H1 kinase; D018844:Cyclin-Dependent Kinases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde