Activation of multiple protein kinases during the burst in protein phosphorylation that precedes the first meiotic cell division in Xenopus oocytes

Abstract

A number of different protein and peptide substrates were used to identify and characterize stimulated kinase activities in Xenopus oocyte extracts prepared during the major burst in protein phosphorylation that precedes meiotic cell division. While total cAMP-dependent protein kinase activity in the cytosol was not stimulated, this kinase was the major kinase phosphorylating a number of the substrates and consequently had to be inhibited to prevent its masking cAMP-independent protein kinase activities. Sizable stimulations of kinase activities were then observed in extracts from progesterone-treated oocytes as compared to controls when the following substrates were utilized: Leu-Arg-Arg-Ala-Ser-Leu-Gly (Kemptide) (8-fold); the synthetic peptide, Arg-Arg-Leu-Ser-Ser-Leu-Arg-Ala, the sequence of which is based on that of a phosphorylation site in ribosomal protein S6 (8-fold); ribosomal protein S6 (8-fold); histone H1 (5-fold); skeletal muscle glycogen synthase (3-fold); and myelin basic protein (30-fold). When these substrates were used to assay extracts fractionated on DEAE-Sephacel, at least three distinct peaks of stimulated kinase activity were detected, eluting at 0.12, 0.17, and 0.21 M NaCl. These peaks were tentatively designated M-phase Activated Kinases(s), MAK-H, MAK-S, and MAK-M, respectively. Using histone H1 as a selective probe for MAK-H and S6 peptide or Kemptide as probes for MAK-S, the kinase activities comprising these peaks were found to cycle with the meiotic cell cycle.