Accumulation of 2'-O-Methylguanosine Deficient tRNATrp in Tryptophan Limited Saccharomyces cerevisiae

SUMMARY: Saccharomyces cerevisiae synthesizes one major tryptophan transfer ribonucleic acid (tRNATrp) species (isoacceptor A) carrying characteristic base modifications. Under tryptophan limited growth conditions wild-type strain X2180-1A exhibited a second important tRNATrp species (isoacceptor B). The total amount of tRNATrp, approximately 2.5 pmol (mg dry wt)-1, stayed essentially constant during amino acid shift-down experiments. The amount of isoacceptor B relative to total tRNATrp was 10 to 15% during amino acid sufficient exponential growth conditions, but increased during tryptophan limitation three- to four-fold. Analysis of the base compositions showed that isoacceptor B differed from isoacceptor A in one respect only: 2′-O-methylguanosine, a modified guanosine base occurring at position 17 of the major isoacceptor A tRNATrp, was not detectable in hydrolysates of purified isoacceptor B. The biological significance of isoacceptor B is discussed.