Alteration of the Q family of transfer RNAs in adult Drosophila melanogaster as a function of age, nutrition, and genotype.

Four tRNAs are known to contain Q, a hypermodified form of guanosine, in one of their isoacceptor forms; these are tRNATyr, tRNAHis, tRNAAsp, and tRNAAsn. The first three have been examined in Drosophila melanogaster at different ages in four genotypes. As the adult flies age, the ratio of the Q/non-Q isoacceptors increases, and the rate of increase is more rapid for Samarkand than for Oregon-R (two wild-type strains). Similarly, two other strains that carry the mutations su(s)2 v; bw and v; bw also differ in the rate of isoacceptor alteration. Diet has a marked effect on the ratio of Q/non-Q isoacceptors for each tRNA. tRNALeu does not change with age or diet and is believed not to contain Q in any of its isoacceptors. The possible role of Q in altering the rate of protein synthesis was examined in a cell-free, tRNA-dependent, mRNA-dependent system. No essential effect on the rate or extent of protein synthesis was detected upon comparison of Q-enriched or Q-deficient tRNA. The ratio of Q/non-Q isoacceptors for these tRNAs is clearly controlled by age-related and diet-related mechanisms that can modulate the amount of Q in the tRNA. The relationship of these studies to Strehler's hypothesis of age-related control of protein synthesis is discussed.