Isolation of eukaryotic ribosomal proteins: purification and characterization of S25 and L16

Proteins were extracted from rat liver ribosomal subunits with ethanol and ammonium chloride. The extract from the 40S subunit contained mainly S25, but smaller amounts of a number of other proteins were found as well; the extract from the 60S subparticle had L16 in addition to P1, P2, S25, and several other proteins. S25 and L16 had not been purified before. The former was isolated from the ethanol-ammonium chloride extract by stepwise elution from carboxymethylcellulose with LiCl, chromatography on phosphocellulose, and filtration through Sephadex G-75; L16 was purified by elution from carboxymethylcellulose with LiCl (in steps). The molecular weight of the two proteins was estimated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate; and amino acid composition was determined also.