Characterization of glycine-rich proteins from the ribonucleoproteins containing heterogeneous nuclear ribonucleic acid.

The salt-soluble 28 000-38 000-dalton proteins were isolated from ribonucleoproteins containing heterogeneous nuclear RNA and partially purified. They were glycine-rich proteins (22-26 mol/100) and contained a small amount of NG-dimethylarginine. Their N-terminal amino acid was blocked. Their pI was basic, extending from 6.95 to 9.20. Some 40 different polypeptides were demonstrated by combining molecular weight and pI determinations. Comparison of peptidic maps and of peptide size after trypsin and thermolysin digestion indicated the presence of only four proteins. The pattern of distribution of pI showing series of discrete major and minor bands common to two or three polypeptides of different apparent molecular weight was also compatible with the existence of four proteins and in addition supported the idea that the multiplicity of polypeptides was due to extensive posttranslational modifications.