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XB-ART-18658
Proc Natl Acad Sci U S A 1996 Jan 09;931:352-6.
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An inhibitor of p34cdc2/cyclin B that regulates the G2/M transition in Xenopus extracts.

Lee TH , Kirschner MW .


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The activity of maturation-promoting factor (MPF), a protein kinase complex composed of p34cdc2 and cyclin B, is undetectable during interphase but rises abruptly at the G2/M transition to induce mitosis. After the synthesis of cyclin B, the suppression of MPF activity before mitosis has been attributed to the phosphorylation of p34cdc2 on sites (threonine-14 and tyrosine-15) that inhibit its catalytic activity. We previously showed that the activity of the mitotic p34cdc2/cyclin B complex is rapidly suppressed when added to interphase Xenopus extracts that lack endogenous cyclin B. Here we show that a mutant of p34cdc2 that cannot be inhibited by phosphorylation (threonine-14-->alanine, tyrosine-15-->phenylalanine) is also susceptible to inactivation, demonstrating that inhibitory mechanisms independent of threonine-14 and tyrosine-15 phosphorylation must exist. We have partially characterized this inhibitory pathway as one involving a reversible binding inhibitor of p34cdc2/cyclin B that is tightly associated with cell membranes. Kinetic analysis suggests that this inhibitor, in conjunction with the kinases that mediate the inhibitory phosphorylations on p34cdc2, maintains the interphase state in Xenopus; it may play an important role in the exact timing of the G2/M transition.

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Species referenced: Xenopus laevis
Genes referenced: ccnb1.2 cdk1

References [+] :
Amon, Regulation of p34CDC28 tyrosine phosphorylation is not required for entry into mitosis in S. cerevisiae. 1992, Pubmed, Xenbase