The activity of protein kinases from hamster fibroblasts towards a synthetic peptide based on a carboxy-terminal portion of ribosomal protein S6.
A synthetic decapeptide, S6(231-240), based on a region near the C-terminus of eukaryotic ribosomal protein S6, was used as a substrate for protein kinases (EC 2.7.1.37) from hamster fibroblasts stimulated with fresh medium. Consistent with the results of others using shorter peptides from this region, it was found that the cyclic AMP-dependent protein kinase preferentially phosphorylated the residue corresponding to Ser-235, whereas protein kinase C preferentially phosphorylated the residue corresponding to Ser-236 in this peptide. The peptide did not serve as a substrate for the growth-associated protein kinase from hamster fibroblasts that phosphorylated ribosomal protein S6 in 40S ribosomal subunits, but did serve as a substrate for a previously undetected protein kinase activity that was resolved from the latter by DEAE-cellulose chromatography. This S6(231-240) protein kinase activity did not phosphorylate ribosomal protein S6 in 40S ribosomal subunits, but is possibly a proteolytic fragment of the 40S ribosomal subunit S6 kinase as the latter activity acquired the ability to phosphorylate the decapeptide after partial tryptic proteolysis. The S6(231-240) protein kinase activity preferentially phosphorylated the residue corresponding to Ser-236 with an apparent Km of 15 microM. These results suggest that specific interactions with the ribosome may be required to activate the growth-associated ribosomal protein S6 kinase.
Department of Biochemistry, University of Glasgow, Scotland, U.K.
J
J
Munro
D G
DG
Campbell
D P
DP
Leader
D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D006224:Cricetinae; D005347:Fibroblasts / Q000201:enzymology; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism; D010455:Peptides / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D038601:Ribosomal Protein S6; D012269:Ribosomal Proteins / Q000378:metabolism*; D012270:Ribosomes / Q000201:enzymology*; D013379:Substrate Specificity; D014357:Trypsin
D010446:Peptide Fragments; D010455:Peptides; D038601:Ribosomal Protein S6; D012269:Ribosomal Proteins; C065817:ribosomal protein S6 (231-240); D011493:Protein Kinase C; D014357:Trypsin