title: Amino acid sequence and sites of phosphorylation in a highly acidic region of nucleolar nonhistone protein C23.
abstract: Novikoff hepatoma nucleolar nonhistone proteins, C23 and B23, contain highly acidic phosphorylated regions (Mamrack, M. D., et al. (1977) Biochem. Biophys. Res. Commun. 76, 150--157). Tryptic peptides from protein C23 containing these regions were purified by DEAE-Sephadex columns and paper electrophoresis at pH 1.8. One of these, peptide C23-Ca, was sequenced by combined automated and conventional methods. The proposed amino acid sequence is shown in eq 1. This peptide was found in three 32P-labeled forms with phosphoryl groups at positions 8 and 25, and probably 28. The highly acidic sequences adjacent to the phosphorylation sites represent a unique class of phosphorylation sites different from those in histones or substrates for cytoplasmic cAMP-dependent kinases. Ala-Ala-Pro-Ala-A5la-Pro-Ala-Ser-Glu-A10sp-Glu-Asp-Glu-Glu-A15sp-Asp-Asp-Asp-Glu-A20sp-Asp-Asp-Asp-Asp-S25er-Gln-Glu-Ser-Glu-G30lu-Glu-Asp-Glu-Glu-V35al-Met-Glu-Ile-Thr-P40ro-Ala-Lys (1).
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002268:Carboxypeptidases; D002466:Cell Nucleolus / Q000032:analysis*; D002868:Chromosomal Proteins, Non-Histone; D008114:Liver Neoplasms, Experimental / Q000032:analysis*; D010446:Peptide Fragments / Q000032:analysis; D010766:Phosphorylation; D051381:Rats
chemical_list: D002868:Chromosomal Proteins, Non-Histone; D010446:Peptide Fragments; D002268:Carboxypeptidases