Methylated amino acids in ribosomal proteins from Escherichia coli treated with ethionine and from a mutant lacking methylation of protein L11.
In the present study, the nature, proportions and distribution of methylated amino acids in ribosomal proteins from Escherichia coli grown in the presence of ethionine and from mutant prm 1 were studied. The undermethylated ribosomes had been labeled by addition in vitro or in vivo of radioactive methyl groups from S-adenosylmethionine or from methionine. The following compounds were identified : N alpha-mono-, di- and trimethylalanines, N epsilon-mono-, di- and trimethyllysines, methylamine and N alpha-trimethylalanyllysine. Except for the latter compound and N-alpha-dimethylalanine, all other derivatives had been previously identified in the literature. It is shown that the dipeptide had been in the past mistaken for N epsilon-monomethyllysine, and arises through incomplete hydrolysis in 24 hrs of the N-terminal peptide bond of protein L11. The results of the present study are discussed in the light of previous work on ribosomal protein methylation by the authors and other workers in the field.