Methylation of ribosomal proteins in HeLa cells

Methylated amino acids from both 40 and 60S subunit proteins of HeLa cytoplasmic ribosome were analyzed. It was observed that methylation of ribosomal proteins occurs in both subunits with N G, N G-dimethylarginine as the major methylated amino acid. The presence of N G, N G-dimethylarginine has been identified by high-voltage paper electrophoresis, by paper chromatography, and by amino acid analysis. In addition, both ribosomal subunits contain methylated lysines with ϵ- N-trimethyllysine being the predominant one, followed by ϵ- N-dimethyllysine. Little, if any ϵ- N-monomethyllysine was detected in either subunit. The cytoplasmic 60S ribosomal subunit contains much more ϵ- N-trimethyllysine compared to the 40S ribosomal subunit. The possible biological significance of methylation was discussed.