Genetics of ribosomal protein methylation in Escherichia coli. II. A mutant lacking a new type of methylated amino acid, N5-methylglutamine, in protein L3.

The ribosomes of an Escherichia coli mutant, designated prm-2, can be methylated in vitro by an enzymatic fraction from wild-type. This enzyme is inactive on the ribosomes from another mutant, prm-1, is reported previously to be methyl group-deficient in protein L11. In vitro methylation of prm-2 ribosomes resulted in the incorporation of about one methyl group per molecule of protein L3. After acid hydrolysis, all the methyl groups were found in a very basic compound which was identified as methylamine. This compound could have been generated by acid hydrolysis of N-methylated amide-groups from glutamine or asparagine. Therefore, chemically-synthesized N4-methyl-asparagine and N5-methylglutamine were chromatographed together with an enzymatic hydrolysate of methylated prm-2 proteins. In all the chromatogrphic systems studied the methylated amino acid was found in the same position as N5'-methylglutamine. These results indicate that mutant prm-2 lacks one residue of N5-methylglutamine present in ribosomal protein L3 of wild type E. coli.