The Effects of Histidine Starvation on the Methylation of Ribosomal RNA

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Abstract
The effect of amino acid starvation on the control of ribosome biosynthesis at the post-transcriptional level was studied in [mouse] Ehrlich ascites cells. A comparison of the tunrover rates of ribosomal precursor RNA (pre-rRNA) and the degree of methylation of ribosomal RNA after histidine deprivation revealed that the slow down of ribosome formation is accompanied by a significant inhibition of rRNA methylation. Analysis of nucleolar and cytoplasmic RNA double-labeled with L-[Me-3H]methionine and [14C]uridine, as well as a quantitative determination of alkali-stable dinucleotides on DEAE-Sephadex, showed that methylation of rRNA species was inhibited by about 50% under shift-down conditions. This decrease in RNA methylation does not reflect an inhibition of rRNA methylases caused by amino acid starvation but is rather brought about by a shrinkage in the pool size of S-adenosylmethionine, the donor of methyl groups. Amino acid starvation might exert its blocking effect on proper ribosome maturation by affecting the methylation of 45-S RNA.