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XB-ART-24685
Mol Cell Biol 1991 Aug 01;118:3860-7. doi: 10.1128/mcb.11.8.3860-3867.1991.
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Phosphorylation of Xenopus cyclins B1 and B2 is not required for cell cycle transitions.

Izumi T , Maller JL .


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The cdc2 kinase and B-type cyclins are known to be components of maturation- or M-phase-promoting factor (MPF). Phosphorylation of cyclin B has been reported previously and may regulate entry into and exit from mitosis and meiosis. To investigate the role of cyclin B phosphorylation, we replaced putative cdc2 kinase phosphorylation sites in Xenopus cyclins B1 and B2 by using oligonucleotide site-directed mutagenesis. We found that Ser-90 of cyclin B2 and Ser-94 or Ser-96 of cyclin B1 are the main phosphorylation sites both in functional Xenopus egg extracts and after phosphorylation with purified MPF in vitro. Microtubule-associated protein (MAP) kinase from Xenopus eggs phosphorylated cyclin B1 significantly at Ser-94 or Ser-96, whereas it was largely inactive against cyclin B2. The substitutions that ablated phosphorylation at these sites, however, resulted in no functional differences between mutant and wild-type cyclin, as judged by the kinetics of M-phase degradation, induction of mitosis in egg extracts, or induction of oocyte maturation. These results indicate that the phosphorylation of Xenopus B-type cyclins by cdc2 kinase or MAP kinase is not required for the hallmark functions of cyclin.

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Species referenced: Xenopus
Genes referenced: ccnb1 ccnb1.2 ccnb2 cdk1 mapk1

References [+] :
Anderson, Processing of adenovirus 2-induced proteins. 1973, Pubmed