Mitogen-activated Swiss mouse 3T3 RSK kinases I and II are related to pp44mpk from sea star oocytes and participate in the regulation of pp90rsk activity.
Using a recombinant rsk gene product as a substrate for in vitro kinase assays, we have identified two mitogen-activated Swiss 3T3 RSK protein kinase activities (referred to as RSK kinase I and RSK kinase II, based on their order of elution from phenyl-Sepharose). Polyclonal antisera prepared against maturation-regulated 44-kDa myelin basic protein (MBP) kinase (pp44mpk) purified from sea star oocytes demonstrated immunocrossreactivity with polypeptides of approximately 44 kDa in the RSK kinase I preparation and approximately 42 kDa in the RSK kinase II preparation, respectively. These polypeptides were also recognized by anti-phosphotyrosine antibodies, and either phosphatase 1B or 2A (tyrosine- and serine/threonine-specific phosphatases, respectively) separately inactivated RSK phosphotransferase activity supporting the notion that tyrosine and serine/threonine phosphorylation are required for activity. In vitro, both RSK kinases and MBP kinase phosphorylated recombinant RSK and generated nearly identical two-dimensional tryptic phosphopeptide maps. They also phosphorylated MBP and microtubule-associated protein 2 but not 40S ribosomal protein S6. Furthermore, these protein kinases phosphorylated and partially activated pp90rsk in immune complexes obtained from quiescent cells.
Chung
J
J
Department of Cellular and Molecular Physiology, Harvard Medical School, Boston, MA 02115.
Pelech
S L
SL
Blenis
J
J
D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D002852:Chromatography, Ion Exchange; D004789:Enzyme Activation; D007700:Kinetics; D051379:Mice; D008970:Molecular Weight; D009865:Oocytes / Q000201:enzymology; D010449:Peptide Mapping; D010748:Phosphopeptides / Q000302:isolation & purification; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D013215:Starfish / Q000201:enzymology*
D010748:Phosphopeptides; D011994:Recombinant Proteins; D011494:Protein Kinases; D019893:Ribosomal Protein S6 Kinases; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C512964:Rps6ka1 protein, mouse; C069330:ribosomal protein S6 kinase, 90kDa, polypeptide 3