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Cdc2 is the cyclin-dependent kinase that controls entry of cells into mitosis. Phosphorylation of Cdc2 on threonine-14 and tyrosine-15 inhibits the activity of the enzyme and prevents premature initiation of mitosis. Although Wee1 has been identified as the kinase that phosphorylates tyrosine-15 in various organisms, the threonine-14-specific kinase has not been isolated. A complementary DNA was cloned from Xenopus that encodes Myt1, a member of the Wee1 family that was discovered to phosphorylate Cdc2 efficiently on both threonine-14 and tyrosine-15. Myt1 is a membrane-associated protein that contains a putative transmembrane segment. Immunodepletion studies suggested that Myt1 is the predominant threonine-14-specific kinase in Xenopus egg extracts. Myt1 activity is highly regulated during the cell cycle, suggesting that this relative of Wee1 plays a role in mitotic control.
Mueller et al. (Fri,) studied this question.