Dephosphorylation and activation of Xenopusp34cdc2 protein kinase during the cell cycle

Abstract

Genetic studies in the fission yeast Schizosaccharomyces pombe have established that a critical element required for the G2----M-phase transition in the cell cycle is encoded by the cdc2+ gene. The product of this gene is a serine/threonine protein kinase, designated p34cdc, that is highly conserved functionally from yeast to man2 and has a relative molecular mass of 34,000 (34 K). Purified maturation-promoting factor (MPF) is a complex of p34cdc2 and a 45K substrate that appears in late G2 phase and is sufficient to drive cells into mitosis. This factor has been identified in all eukaryotic cells, and in vitro histone H1 is the preferred substrate for phosphorylation. The increase in the activity of H1 kinase in M-phase is associated with a large increase in total cell protein phosphorylation which is believed to be a consequence of MPF activation. We show here that the H1 kinase activity of p34cdc2 oscillates during the cell cycle in Xenopus, and maximal activity correlates with the dephosphorylated state of p34cdc2. Direct inactivation of MPF in vitro is accompanied by phosphorylation of p34cdc2 and reduction of its protein kinase activity.

A novel ubiquitin carboxyl terminal hydrolase is involved in toad oocyte maturation

“…The concentration of cyclin B increases steadily from late S phase up to its peak at the phase transition point from G 2 to M, whereas the level of p34 cdc2 remains relatively constant throughout the cell cycle [5], [6]. The modulation of cyclin concentration by synthesis and degradation is of special importance for the control of MPF (maturation/M-phase promoting factor) activity [7].…”

cdc2 phosphorylation is required for its interaction with cyclin

“…On the other hand the phosphorylation of cdc2 changes during the cell cycle Gautier et al, 1989;Gould et al, 1990;Gould and Nurse, 1989; Krek and Nigg, 1991). In mammalian cells, fission yeast and Xenopus oocytes, the tyrosine dephosphorylation of cdc2 parallels its activation (Dunphy and Newport, 1989; Gould et al, 1990;Gould and Nurse, 1989;Morla et al, 1989).…”

In vitro fusion of endocytic vesicles is inhibited by cyclin A-cdc2 kinase.

“…Entry of cells into mitosis is initiated by activation of cdc2 kinase, which requires binding of cyclin to the p34 catalytic subunit Pines and Hunter, 1989) and posttranslational modification (Dunphy and Newport, 1989;Gautier et al, 1989;Gould and Nurse, 1989;Ducommun et al, 1991;Gautier and Maller, 1991;Gould et al, 1991;Norbury et al, 1991). A-and B-type cyclins accumulate during interphase, rising to maximum levels at the G2-M transition (Evans et al, 1983) when activation of cdc2 kinase occurs.…”