Characterization of methylated neutral amino acids from Escherichia coli ribosomes

Abstract

The methylated neutral amino acids from both 30S and 50S ribosomal subunits of an Escherichia coli K strain were characterized. The 508 ribosomal subunit contains three methylated neutral amino acids: N-monomethylalanine, N-monomethylmethionine, and an as yet unidentified methylated amino acid found in protein Lll. Both N-monomethylalanine and N-monomethylmethionine were found in protein L33. The amount ofN-monomethylmethionine in this protein, however, is variable but not more than 0.25 molecules per protein. Thus protein L33 from this E. coli K strain has heterogeneity in its N-terminal amino acid and can start with eitherN-monomethylalanine or N-monomethylmethionine. The N-monomethylmethionine residue was not derived from the reduction ofN-formylmethionine in the protein. The 30S ribosomal subunit contains only one methylated neutral amino acid: N-monomethylalanine.

Modification of yeast ribosomal proteins. Methylation

“…A similar difference between both types of subunits has been observed in HeLa cells (Chang et al, 1976), whereas in E. coli hardly any methylated arginine residues have been found (Chang & Chang, 1975). Recently, the occurrence of a-N-monomethylated methionine and alanine residues in the ribosomal proteins of E. coli has been reported (Chen et al, 1977;Chang & Budzilowicz, 1977). Therefore the slightly higher 3H/14C ratio of the material on the electrophoretogram migrating in the region of the neutral amino acids (compound X in Fig.…”

Methylation of proteins involved in translation

“…after ribosome assembly) (Goldenberg and Eliceiri, 1977;Scolnik and Eliceiri, 1979). Interestingly, in vitro labelling data of Scolnik and Eliceiri (1979) suggested that modification of some RP site(s) may involve a Me donor other than (Alix and Hayes, 1974;1975;1976b;Chang and Budzilowicz, 1977;Dognin and Wittmann-Liebold, 1977;Lederer et al, 1977;Hernandez and Cannon, 1978;Lhoest and Colson, 1981;Van Noort et al, 1986). Similarly, singleand double-labelling procedures in vivo were used to determine which of the S. cerevisiae RPs were methylated (Cannon et al, 1977;Kruiswijk et al, 1978;Lhoest et al, 1984).…”

“…The following two different IF3 isoforms are detected during protein purification: the major one, with N-monomethylated Met; and the minor one with cleaved Met. This is reminiscent of methylation of the bacterial L33 that had a heterogeneity at its N-terminus containing two types of molecules: N-Me-Ala or N-Me-Met (Chang and Budzilowicz, 1977); however, the IF3 penultimate residue is Lys. It is not clear which isoform of IF3 is more active and how the lack of N-monomethylated Met affects IF3 function.…”

“… The E. coli RPs were initially shown to be methylated by double‐labelling experiments in vivo , using [1– 14 C]methionine and [methyl‐ 3 H]methionine (Alix and Hayes, 1974; Chang and Chang, 1974; Chang et al ., 1974; 1975; 1976b; Chang and Budzilowicz, 1977; Chen et al ., 1977; Dognin and Wittmann‐Liebold, 1977; Lederer et al ., 1977; Hernandez and Cannon, 1978; Lhoest and Colson, 1981; Van Noort et al ., 1986). Similarly, single‐ and double‐labelling procedures in vivo were used to determine which of the S. cerevisiae RPs were methylated (Cannon et al ., 1977; Kruiswijk et al ., 1978; Lhoest et al ., 1984).…”