Activation of human CDC2 protein as a histone H1 kinase is associated with complex formation with the p62 subunit.
p34 kinase, the product of the CDC2 gene, is a cell-cycle regulated protein kinase that is most active during mitosis. In HeLa cells, p34 kinase has previously been shown to exist in both a low- and a high-molecular-mass form, the latter of which is only found in cells in the G2/M phase of the cell cycle and contains a 62-kDa subunit. Here we show that although each form of the kinase phosphorylates casein in vitro, only the high-molecular-mass form uses histone H1 as substrate. The high-molecular-mass form of p34 kinase from nocodazole-treated HeLa cells was purified 6700-fold. The apparent molecular mass of the mitotic CDC2-encoded protein kinase complex was 220 kDa. The purified enzyme phosphorylated not only its endogenous 62-kDa subunit but also phosphorylated histone H1 with a Km of 3 microM and used ATP 40 times more efficiently than GTP (Km 54 microM and 2 mM, respectively). The enzyme activity was unaffected by cAMP, calcium/calmodulin, or by the heat-stable inhibitor of cAMP-dependent protein kinase. These characteristics are typical of growth-associated histone H1 kinase from different organisms. These results suggest that CDC2 protein may be activated as an M-phase-specific protein kinase in part by its association with the p62 subunit.
Brizuela
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Cold Spring Harbor Laboratory, NY 11724.
Draetta
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G
Beach
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D
D016203:CDC2 Protein Kinase; D002453:Cell Cycle; D002848:Chromatography, DEAE-Cellulose; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D004789:Enzyme Activation; D006367:HeLa Cells / Q000166:cytology / Q000201:enzymology; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D008970:Molecular Weight; D010750:Phosphoproteins / Q000302:isolation & purification / Q000378:metabolism*; D006656:Protamine Kinase / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D013379:Substrate Specificity
D046911:Macromolecular Substances; D010750:Phosphoproteins; D011494:Protein Kinases; D006656:Protamine Kinase; D016203:CDC2 Protein Kinase