Open AccessA protein kinase from Xenopus eggs specific for ribosomal protein S6.
Author(s) -
Eleanor Erikson,
James L. Maller
Publication year - 1985
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.82.3.742
Subject(s) - ribosomal protein s6 , phosvitin , ribosomal protein , protein kinase a , biochemistry , biology , microbiology and biotechnology , protein phosphorylation , casein kinase 2 , phosphorylation , mitogen activated protein kinase kinase , ribosome , rna , gene
A protein kinase specific for ribosomal protein S6 has been purified from eggs of Xenopus laevis. As visualized on a silver-stained polyacrylamide gel, the major protein in the preparation migrated with a Mr of 90,000. Incubation of the enzyme preparation with [gamma-32P]ATP led to phosphorylation of this protein on serine residues. Upon glycerol gradient centrifugation, the S6 kinase activity and the Mr 90,000 protein both sedimented with a Mr of 50,000-55,000. Two-dimensional gel electrophoresis demonstrated that up to 4-5 phosphate groups per S6 molecule could be incorporated with this enzyme in vitro, and two-dimensional peptide mapping demonstrated that the phosphopeptides from S6 labeled in vitro with the enzyme comigrated with those from highly phosphorylated S6 labeled in vivo in response to progesterone treatment. The purified S6 protein kinase did not phosphorylate at a significant rate ribosomal protein S10, histone H1, histone H4, mixed histones, casein, or phosvitin, indicating a high degree of substrate specificity. These results indicate that activation of a single S6 protein kinase may be sufficient to account for increased S6 phosphorylation after a growth stimulus.