Properties of ribosomal proteins from two mammalian sources.

1. Ribosomal protein fractions from rabbit reticulocytes and rat liver were prepared by extracting ribosomes with 0.2n-hydrochloric acid or guanidinium chloride and subsequent dialysis. 2. Treatment for 2.5hr. or less with 0.2n-hydrochloric acid dissolved 46-54% of the proteins, which were richer in arginine and lysine and in N-terminal alanine groups and poorer in aspartic acid and glutamic acid and in N-terminal glycine groups than the acid-insoluble proteins. 3. Protein fractions prepared from the guanidinium chloride extract of ribosomes from rat liver were usually more basic than those from rabbit reticulocytes. 4. The ratios lysine: arginine of fractions in the guanidinium chloride extracts were appreciably higher for proteins from rabbit reticulocytes than from rat liver. 5. The concentration of urea and the pH of the gel affected the rate of migration and number of bands in starch-gel electrophoresis.