50-S Ribosomal Proteins.

Peptide studies on two acidic proteins, A₁ and A₂, from 50-S ribosomes of Escherichia coli indicate a closely related primary structure. 1. Amino acid compositions of the tryptic peptides of the two proteins are identical, with exception of the amino terminal peptide. 2. The N-terminal amino acid sequence of A₂-protein is Ser-Ile-Thr-Lys, while that of A₁-protein is N-acetyl-Ser-Ile-Thr-Lys. 3. The estimated number of 120 amino acid residues in each polypeptide chain is consistent with the physical molecular weight estimate. 4. In 50% of the polypeptide chains, in both A₁- or A₂-protein, a specific lysine residue is replaced by ε-N-monomethyl-lysine. [ABSTRACT FROM AUTHOR]