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Substrate specificity of ribosomal protein S6 kinase II from Xenopus eggs. 1988

E Erikson, and J L Maller
Department of Pharmacology, University of Colorado School of Medicine, Denver 80262.

The substrate specificity of ribosomal protein S6 kinase II (S6 K II) from Xenopus eggs was evaluated using several protein substrates and a synthetic peptide corresponding to two phosphorylation sites in ribosomal protein S6. Previous studies had shown that S6 K II is unable to phosphorylate histones, casein, or phosvitin, proteins commonly used as substrates for protein kinases. In the present study S6 K II was found to phosphorylate with a significant stoichiometry rabbit skeletal muscle glycogen synthase, cardiac and skeletal muscle troponin I, and lamin C. In addition, the S6 peptide was phosphorylated by S6 K II to the same extent as observed with the catalytic subunit of cAMP-dependent protein kinase. Studies with oocytes undergoing progesterone-induced meiotic maturation and with activated or fertilized eggs revealed identical oscillations in both S6 and lamin C kinase activity. These results indicate that S6 K II does not have an absolute specificity for S6 in vitro. Therefore, since this enzyme is regulated during the cell cycle, it may phosphorylate several other proteins of interest during mitogenic stimulation.

UI MeSH Term Description Entries
D011494 Protein Kinases A family of enzymes that catalyze the conversion of ATP and a protein to ADP and a phosphoprotein. Protein Kinase,Kinase, Protein,Kinases, Protein
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D012270 Ribosomes Multicomponent ribonucleoprotein structures found in the CYTOPLASM of all cells, and in MITOCHONDRIA, and PLASTIDS. They function in PROTEIN BIOSYNTHESIS via GENETIC TRANSLATION. Ribosome
D013379 Substrate Specificity A characteristic feature of enzyme activity in relation to the kind of substrate on which the enzyme or catalytic molecule reacts. Specificities, Substrate,Specificity, Substrate,Substrate Specificities
D014982 Xenopus laevis The commonest and widest ranging species of the clawed "frog" (Xenopus) in Africa. This species is used extensively in research. There is now a significant population in California derived from escaped laboratory animals. Platanna,X. laevis,Platannas,X. laevi
D019893 Ribosomal Protein S6 Kinases A family of protein serine/threonine kinases which act as intracellular signalling intermediates. Ribosomal protein S6 kinases are activated through phosphorylation in response to a variety of HORMONES and INTERCELLULAR SIGNALING PEPTIDES AND PROTEINS. Phosphorylation of RIBOSOMAL PROTEIN S6 by enzymes in this class results in increased expression of 5' top MRNAs. Although specific for RIBOSOMAL PROTEIN S6 members of this class of kinases can act on a number of substrates within the cell. The immunosuppressant SIROLIMUS inhibits the activation of ribosomal protein S6 kinases. S6 Kinase,Ribosomal Protein S6 Kinase,S6-H4 Kinase,S6 H4 Kinase

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