The primary structure of the acidic phosphoprotein P2 from rat liver 60 S ribosomal subunits. Comparison with ribosomal 'A' proteins from other species.

The primary structure of rat liver ribosomal protein P2 was deduced from the sequence of the peptides. Ten peptides were obtained by cleavage of P2 with trypsin. The peptides, which accounted for the 111 residues of P2, were isolated by high voltage electrophoresis and chromatography on cellulose thin layer sheets, and the partial or complete sequence was determined by micromanual or solid-phase procedures using 4-N,N-dimethylaminoazobenzene 4'-isothiocyanate and phenylisothiocyanate. In a similar manner, the sequence of 14 peptic peptides was determined. The sequence of the NH2-terminal 30 residues of P2 was obtained by automatic Edman degradation in a sequenator. The ordering of the tryptic peptides was aided by determination of the partial or complete sequence of fragments generated with chymotrypsin, or Armillaria mellea protease, or by secondary cleavage of peptic peptides with trypsin. The carboxyl-terminal sequence was obtained from a cyanogen bromide fragment and from hydrolysis with carboxypeptidase. The sequence of protein P3 was also determined. P3 differs from P2 only in that it lacks the carboxyl-terminal 8 residues, and hence, it is likely to be a proteolytic product of P2. Rat liver ribosomal protein P2 is homologous with yeast YP A1, with Artemia salina eL12, and with Halobacterium cutirubrum L20. It is likely that rat liver P2 is also homologous with the prokaryotic ribosomal "A" proteins, Escherichia coli L7/L12, Micrococcus lysodeikticus MA1, and Bacillus subtilis L9, but that during evolution, a transposition of a portion of the molecule occurred.