A- and B-type cyclins differentially modulate substrate specificity of cyclin-cdk complexes.
Both cyclins A and B associate with and thereby activate cyclin-dependent protein kinases (cdks). We have investigated which component in the cyclin-cdk complex determines its substrate specificity. The A- and B-type cyclin-cdk complexes phosphorylated histone H1 and their cyclin subunits in an indistinguishable manner, irrespective of the catalytic subunit, p33cdk2 or p34cdc2. In contrast, only the cyclin A-cdk complexes phosphorylated the Rb-related p107 protein in vitro. Likewise, binding studies revealed that cyclin A-cdk complexes bound stably to p107 in vitro, whereas cyclin B-cdk complexes did not detectably associate with p107, under identical assay conditions. Binding to p107 required both cyclin A and a cdk as neither subunit alone bound to p107. These results demonstrate that although the kinase subunit provides a necessary component for binding, it is the cyclin subunit that plays the critical role in targeting the complex to p107. Finally, we show that the cyclin A-p33cdk2 complex phosphorylated p107 in vitro at most of its sites that are also phosphorylated in human cells, suggesting that the cyclin A-p33cdk2 complex is a major kinase for p107 in vivo.
Department of Molecular Carcinogenesis, Sylvius Laboratory, University of Leiden, The Netherlands.
D S
DS
Peeper
L L
LL
Parker
M E
ME
Ewen
M
M
Toebes
F L
FL
Hall
M
M
Xu
A
A
Zantema
A J
AJ
van der Eb
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Piwnica-Worms
D000818:Animals; D016367:Baculoviridae; D001483:Base Sequence; D016203:CDC2 Protein Kinase; D002478:Cells, Cultured; D016213:Cyclins / Q000502:physiology*; D006801:Humans; D008969:Molecular Sequence Data; D009036:Moths; D009687:Nuclear Proteins; D009841:Oligonucleotides; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism; D050720:Retinoblastoma-Like Protein p107
D016213:Cyclins; D009687:Nuclear Proteins; D009841:Oligonucleotides; D011506:Proteins; C493844:RBL1 protein, human; D050720:Retinoblastoma-Like Protein p107; D011494:Protein Kinases; D016203:CDC2 Protein Kinase