title: The RRASK motif in Xenopus cyclin B2 is required for the substrate recognition of Cdc25C by the cyclin B-Cdc2 complex.
abstract: The FLRRXSK sequence is conserved in the second cyclin box fold of B-type cyclins. We show that this conserved sequence in Xenopus cyclin B2, termed the RRASK motif, is required for the substrate recognition by the cyclin B-Cdc2 complex of Cdc25C. Mutations to charged residues of the RRASK motif of cyclin B2 abolished its ability to activate Cdc2 kinase without affecting its capacity to bind to Cdc2. Cdc2 bound to the cyclin B2 RRASK mutant was not dephosphorylated by Cdc25C, and as a result, the complex was inactive. The cyclin B2 RRASK mutants can form a complex with the constitutively active Cdc2, but a resulting active complex did not phosphorylate a preferred substrate Cdc25C in vitro, although it can phosphorylate the non-specific substrate histone H1. The RRASK mutations prevented the interaction of Cdc25C with the cyclin B2-Cdc2 complex. Consistently, the RRASK mutants neither induced germinal vesicle breakdown in Xenopus oocyte maturation nor activated in vivo Cdc2 kinase during the cell cycle in mitotic extracts. These results suggest that the RRASK motif in Xenopus cyclin B2 plays an important role in defining the substrate specificity of the cyclin B-Cdc2 complex.
authors.affiliation: Department of Molecular Biology, Graduate School of Medical Sciences, Kyushu University, Maidashi, Fukuoka 812-8582, Japan.
authors.forename: Tadahiro
authors.initials: T
authors.lastname: Goda
authors.forename: Takashi
authors.initials: T
authors.lastname: Ishii
authors.forename: Nobushige
authors.initials: N
authors.lastname: Nakajo
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Sagata
authors.forename: Hideki
authors.initials: H
authors.lastname: Kobayashi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism*; D017124:Conserved Sequence; D019926:Cyclin B / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D006657:Histones / Q000378:metabolism; D007163:Immunosorbent Techniques; D016296:Mutagenesis; D009865:Oocytes / Q000187:drug effects / Q000502:physiology; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D014982:Xenopus laevis; D020687:cdc25 Phosphatases / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D019926:Cyclin B; D006657:Histones; D016203:CDC2 Protein Kinase; D020687:cdc25 Phosphatases