Mos stimulates MAP kinase in Xenopus oocytes and activates a MAP kinase kinase in vitro.
Several protein kinases, including Mos, maturation-promoting factor (MPF), mitogen-activated protein (MAP) kinase, and MAP kinase kinase (MAPKK), are activated when Xenopus oocytes enter meiosis. De novo synthesis of the Mos protein is required for progesterone-induced meiotic maturation. Recently, bacterially synthesized maltose-binding protein (MBP)-Mos fusion protein was shown to be sufficient to initiate meiosis I and MPF activation in fully grown oocytes in the absence of protein synthesis. Here we show that MAP kinase is rapidly phosphorylated and activated following injection of wild-type, but not kinase-inactive mutant, MBP-Mos into fully grown oocytes. MAP kinase activation by MBP-Mos occurs within 20 min, much more rapidly than in progesterone-treated oocytes. The MBP-Mos fusion protein also activates MPF, but MPF activation does not occur until approximately 2 h after injection. Extracts from oocytes injected with wild-type but not kinase-inactive MBP-Mos contain an activity that can phosphorylate MAP kinase, suggesting that Mos directly or indirectly activates a MAPKK. Furthermore, activated MBP-Mos fusion protein is able to phosphorylate and activate a purified, phosphatase-treated, rabbit muscle MAPKK in vitro. Thus, in oocytes, Mos is an upstream activator of MAP kinase which may function through direct phosphorylation of MAPKK.
Fred Hutchinson Cancer Research Center, Seattle, Washington 98104.
J
J
Posada
N
N
Yew
N G
NG
Ahn
G F
GF
Vande Woude
J A
JA
Cooper
D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D004789:Enzyme Activation; D008845:Microinjections; D008938:Mitosis; D009865:Oocytes / Q000201:enzymology; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D017231:Proto-Oncogene Proteins c-mos / Q000378:metabolism*; D014982:Xenopus laevis / Q000196:embryology*
D010750:Phosphoproteins; D011494:Protein Kinases; D017231:Proto-Oncogene Proteins c-mos; D017871:Calcium-Calmodulin-Dependent Protein Kinases