Isolation of eukaryotic ribosomal proteins. Purification and characterization of the 60 S ribosomal subunit proteins La, Lb, Lf, P1, P2, L13', L14, L18', L20, and L38.

The proteins of the large subunit of rat liver ribosomes were separated into seven groups by stepwise elution from carboxymethylcellulose with LiCl at pH 6.5. Ten proteins (La, Lb, Lf, P1, P2, L13', L14, L18', L20, and L38) were isolated from three groups (A60, B60, and D60) by ion exchange chromatography on carboxymethylcellulose and DEAE-cellulose, and by filtration through Sephadex. The amount of protein obtained varied from 0.3 to 3.8 mg. Two of the proteins (La and L18') had no detectable contamination; the impurities in the others were not greater than 8%. The molecular weight of the proteins was estimated by polyacrylamide gel electrophoresis in sodium dodecyl sulfate; the amino acid composition was determined. Several additional acidic proteins were identified: P1a and P1b are phosphorylated derivatives of P1; P2a, P2b, and P2c are phosphorylated derivatives of P2. P1 and P2 are distinct proteins but both have large amounts of alanine (20.4 and 17.5 mol %).