The methyl groups in ribosomal RNA from Escherichia coli

Abstract

1. (1) Escherichia coli cells were labeled with [ Me- 14C]methionine and [ 3H]adenosine in the presence or absence of chloramphenicol. The ratio of 14C to 3H in RNA was taken as a measure of the extent of methylation of the RNA molecules. Methylation of mature 16-S ribosomal RNA (rRNA) was about 60 % higher than that of mature 23-S rRNA. The degrees of methylation of nascent 23-S and nascent 16-S rRNA formed in the presence of chloramphenicol were 56 and 12 % of the corresponding values for mature 23-S and 16-S rRNA, respectively. The methylation of transfer RNA (tRNA) was not significantly inhibited in the presence of chloramphenicol. 2. (2) Paper autoradiograms of nucleotides produced by alkaline hydrolysis of Me- 14C-labeled RNA revealed a significant difference between mature 23-S and 16-S rRNA. The distribution of methyl groups in nascent 23-S (or 16-S) rRNA from chloramphenicol particles was qualitatively similar to that in mature 23-S (or 16-S) rRNA. Methylation of certain component nucleotides of the rRNA was found to be more or less selectively arrested in the presence of chloramphenicol. The autoradiogram of hydrolysates of tRNA was very different from that for rRNA. 3. (3) Chromatographic analyses on DEAE-cellulose columns of alkaline hydrolysates of Me- 14C-labeled rRNA and tRNA suggested that the methyl content of the sugar moieties represented not more than 25 % of the total methyl groups in each RNA species.