The role of protein phosphatase type-2A in the Xenopus cell cycle: initiation of the G2/M transition.

The last several years has seen an explosion in the identification of a multiplicity of serine/threonine protein kinases with important functions in eukaryotic cell cycle progression. Although the major serine/threonine phosphoprotein phosphatases, that must oppose the action of the kinases, have been identified and extensively characterized for their involvement in metabolic processes, the functions of the phosphatases in cell cycle regulation is less well established. This paper focuses on the role of the type-2A protein phosphatase (PP2A) in the regulation of the G2/M transition in the Xenopus cell cycle. Although a role for PP2A in regulating G2/M has been suggested by studies in various systems, it is the relative simplicity of the in-vitro cell cycle extracts of Xenopus that has allowed the clearest dissection of the mechanism by which PP2A regulates this transition.