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Joined 2026-09-21 Message
Incoming links: Myt1
CDK1 phosphorylation state 2026-10-14
A CDK1 phosphorylation state identifies modified amino acid residues. Different sites have opposite effects: in studied Xenopus laevis Cdc2, Thr14/Tyr15 are inhibitory, while Thr161 phosphorylation is activating. T denotes a threonine residue, Y a tyrosine residue, and numbers are protein primary structure positions. Do not assume this numbering for every species.[ref]
Role of phosphorylation in p34cdc2 activation: identification of an activating kinase by M. J. Solomon and others. Solomon, Lee and Kirschner (1992), abstract: mapped Xenopus Thr14/Tyr15, loss of activation with Thr161→Ala, and cyclin binding by the triple mutant
The 1992 study supplies a useful separation of mechanisms: replacing Thr14, Tyr15 and Thr161 still permitted cyclin B binding, but replacing Thr161 prevented activation of histone H1 phosphorylation. Binding therefore did not suffice for catalytic activity in that preparation. Activating phosphorylation also occurred with catalytically inactive Cdc2, supporting a separate CDK-activating kinase rather than a requirement for intramolecular autophosphorylation.[ref]
Role of phosphorylation in p34cdc2 activation: identification of an activating kinase by M. J. Solomon and others. Solomon, Lee and Kirschner (1992), abstract: cyclin-binding triple mutant and activating phosphorylation of the kinase-inactive K33R mutant
In this deliberately coarse classification, bound cyclin B, activating phosphorylation, and cleared inhibitory sites must coincide for the activity-permissive state. Removing inhibitory phosphate groups does not supply missing cyclin B or activating phosphorylation. Conversely, adding activating phosphorylation does not erase inhibitory modification. Actual preparations contain mixtures of states and additional regulators; this classification gives no numerical reaction rate.
Myt1 2026-10-14
Myt1 is a protein kinase distinct from Wee1. The cloned Xenopus laevis Myt1 phosphorylated Cdc2 at both inhibitory sites Thr14 and Tyr15; depletion experiments implicated it as the predominant Thr14-directed activity in Xenopus laevis egg extracts.[ref]
Myt1: a membrane-associated inhibitory kinase that phosphorylates Cdc2 on both threonine-14 and tyrosine-15 by P. R. Mueller and others. Mueller, Coleman, Kumagai and Dunphy (1995), abstract: Xenopus clone, both inhibitory sites and immunodepletion result
Wee1 Created 2026-10-14 Updated 2026-10-14
Wee1 is a protein kinase that inhibits CDK1 by adding a phosphate group at an inhibitory site. Purified human Wee1 phosphorylated Cdc2 at Tyr15 in the reported in vitro assay, with no Thr14 modification detected. A catalytic-site mutation abolished both the measured protein kinase activity and the ability to inhibit division. This identifies a catalytic brake rather than merely a correlated protein amount.[ref]
Human Wee1 kinase inhibits cell division by phosphorylating p34cdc2 exclusively on Tyr15 by Clare McGowan and others. McGowan and Russell (1993), abstract: purified human Wee1, Tyr15 specificity, no detectable Thr14 phosphorylation, and Lys114 mutant control
Do not attribute all inhibitory CDK1 phosphorylation to Wee1: the Xenopus laevis Myt1 experiment separately identified activity toward both Thr14 and Tyr15. Nor does every phosphorylation inhibit its target: activating Thr161 modification in the studied Xenopus laevis Cdc2 has the opposite role. In cell-cycle activation feedback, suppression of Wee1 removes a brake on CDK1, reinforcing the transition without implying that the total amount of either protein instantly disappears.