title: Multiple roles for protein phosphatase 1 in regulating the Xenopus early embryonic cell cycle.
abstract: Using cytostatic factor metaphase II-arrested extracts as a model system, we show that protein phosphatase 1 is regulated during early embryonic cell cycles in Xenopus. Phosphatase 1 activity peaks during interphase and decreases shortly before the onset of mitosis. A second peak of activity appears in mitosis at about the same time that cdc2 becomes active. If extracts are inhibited in S-phase with aphidicolin, then phosphatase 1 activity remains high. The activity of phosphatase 1 appears to determine the timing of exit from S-phase and entry into M-phase; inhibition of phosphatase 1 by the specific inhibitor, inhibitor 2 (Inh-2), causes premature entry into mitosis, whereas exogenously added phosphatase 1 lengthens the interphase period. Analysis of DNA synthesis in extracts treated with Inh-2, but lacking the A- and B-type cyclins, shows that phosphatase 1 is also required for the process of DNA replication. These data indicate that phosphatase 1 is a component of the signaling pathway that ensures that M-phase is not initiated until DNA synthesis is complete.
authors.affiliation: Howard Hughes Medical Institute, University of Colorado School of Medicine, Denver 80262.
authors.forename: D H
authors.initials: DH
authors.lastname: Walker
authors.forename: A A
authors.initials: AA
authors.lastname: DePaoli-Roach
authors.forename: J L
authors.initials: JL
authors.lastname: Maller
mesh_terms: D000818:Animals; D016590:Aphidicolin / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis / Q000187:drug effects; D004988:Ethers, Cyclic / Q000494:pharmacology; D008938:Mitosis / Q000187:drug effects / Q000502:physiology*; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000502:physiology*; D054645:Protein Phosphatase 1; D014981:Xenopus / Q000196:embryology*
chemical_list: D004988:Ethers, Cyclic; D019319:Okadaic Acid; D016590:Aphidicolin; D004247:DNA; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1