title: Phosphorylation of hepatic ribosomal protein S6 on 80 and 40 S ribosomes. Primary structure of S6 in the region of the major phosphorylation sites for cAMP-dependent protein kinases.
abstract: Rat liver ribosomes and 40 S ribosomal subunits were phosphorylated with the purified catalytic subunit of cAMP-dependent protein kinase. Phosphorylation of ribosomal protein S6 plateaued at around 2 mol of phosphate/mol of protein with both substrates. Peptide map analyses showed that the most prominent phosphorylation sites associated with 40 S substrates were the adjacent serines in the Arg-Leu-Ser-Ser-Leu-Arg segment of S6. The first serine residue appeared to be the preferred site as has been established previously for 80 S ribosomes (Wettenhall, R.E.H., and Cohen, P. (1982) FEBS Lett. 140, 263-269). Additional phosphorylation sites were apparent from the peptide maps. One of these was associated with the triphosphopeptide (termed T1a) having the sequence Arg-Leu-Ser-Ser-Leu-Arg-Ala-Ser-Thr-Ser-Lys. A larger fragment of S6 (termed Tlc) isolated from mild tryptic digests of whole ribosomes, consisted of the T1a sequence extended by the sequence Ser-Glu-Glu-Ser-Gln-(Lys) at the COOH terminus. A comparison of the size and chromatographic and isoelectric focusing properties of the T1a/T1c peptides and prominent tryptic peptides of S6 from insulin-stimulated hepatocytes indicated a relationship between these peptides. Thus, it appeared that some of the potential phosphorylation sites in the T1a/T1c region of S6 are phosphorylated by an insulin-regulated kinase in hepatocytes.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008970:Molecular Weight; D009132:Muscles / Q000201:enzymology; D010446:Peptide Fragments / Q000032:analysis; D010748:Phosphopeptides / Q000032:analysis; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D038601:Ribosomal Protein S6; D012269:Ribosomal Proteins / Q000302:isolation & purification / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*; D014357:Trypsin
chemical_list: D010446:Peptide Fragments; D010748:Phosphopeptides; D038601:Ribosomal Protein S6; D012269:Ribosomal Proteins; D011494:Protein Kinases; D014357:Trypsin