The N-terminal helix of Xenopus cyclins A and B contributes to binding specificity of the cyclin-CDK complex.
Mitotic cyclins A and B contain a conserved N-terminal helix upstream of the cyclin box fold that contributes to a significant interface between cyclin and cyclin-dependent kinase (CDK). To address its contribution on cyclin-CDK interaction, we have constructed mutants in conserved residues of the N-terminal helix of Xenopus cyclins B2 and A1. The mutants showed altered binding affinities to Cdc2 and/or Cdk2. We also screened for mutations in the C-terminal lobe of CDK that exhibited different binding affinities for the cyclin-CDK complex. These mutations were at residues that interact with the cyclin N-terminal helix motif. The cyclin N-terminal helix mutations have a significant effect on the interaction between the cyclin-CDK complex and specific substrates, Xenopus Cdc6 and Cdc25C. These results suggest that the N-terminal helix of mitotic cyclins is required for specific interactions with CDKs and that to interact with CDK, specific substrates Cdc6 and Cdc25C require the CDK to be associated with a cyclin. The interaction between the cyclin N-terminal helix and the CDK C-terminal lobe may contribute to binding specificity of the cyclin-CDK complex.
Goda
T
T
Department of Molecular Biology, Graduate School of Medical Science, Kyushu University, Fukuoka 812-8582, Japan.
Funakoshi
M
M
Suhara
H
H
Nishimoto
T
T
Kobayashi
H
H
D000595:Amino Acid Sequence; D000818:Animals; D019925:Cyclin A / Q000737:chemistry / Q000378:metabolism*; D019926:Cyclin B / Q000737:chemistry / Q000378:metabolism*; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D014981:Xenopus
D019925:Cyclin A; D019926:Cyclin B; D018844:Cyclin-Dependent Kinases