title: Phosphorylation of the kinase suppressor of ras by associated kinases.
abstract: The kinase suppressor of Ras (KSR) is a loss-of-function allele that suppresses the rough eye phenotype of activated Ras in Drosophila and the multivulval phenotype of activated Ras in Caenorhabditis elegans. The physiological role of mammalian KSR is not known. We examined the mechanisms regulating the phosphorylation of this putative kinase in mammalian cells. Wild-type mouse KSR and a mutated KSR protein predicted to create a kinase-dead protein are phosphorylated identically in intact cells and in the immune complex. Phosphopeptide sequencing identified 10 in vivo phosphorylation sites in KSR, all of which reside in the 539 noncatalytic amino terminal amino acids. Expression of the amino terminal portion of KSR alone demonstrated that it was phosphorylated in the intact cell and in an immune complex in a manner indistinguishable from that of intact KSR. These data demonstrate that the kinase domain of KSR is irrelevant to its phosphorylation state and suggest that the phosphorylation of KSR and its association with a distinct set of kinases may affect intracellular signaling.
authors.affiliation: Eppley Institute for Research in Cancer and Allied Diseases, Department of Biochemistry and Molecular Biology, Omaha, Nebraska 68198-6805, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Volle
authors.forename: J A
authors.initials: JA
authors.lastname: Fulton
authors.forename: O V
authors.initials: OV
authors.lastname: Chaika
authors.forename: K
authors.initials: K
authors.lastname: McDermott
authors.forename: H
authors.initials: H
authors.lastname: Huang
authors.forename: L A
authors.initials: LA
authors.lastname: Steinke
authors.forename: R E
authors.initials: RE
authors.lastname: Lewis
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000936:Antigen-Antibody Complex / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D004622:Embryo, Mammalian; D006801:Humans; D007668:Kidney / Q000166:cytology; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation; D011233:Precipitin Tests; D011489:Protein Denaturation; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D017384:Sequence Deletion; D012694:Serine / Q000235:genetics; D018631:ras Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D000936:Antigen-Antibody Complex; D012694:Serine; D011494:Protein Kinases; C097199:KSR-1 protein kinase; D017346:Protein Serine-Threonine Kinases; D018631:ras Proteins