Queuine-containing isoacceptor of tyrosine tRNA in Drosophila melanogaster. Alteration of levels by divalent cations.

Dietary cadmium causes the queuine-containing, Q(+), isoacceptors to increase relative to the guanine-containing, Q(-), ones of tRNATyr, tRNAHis and tRNAAsp of Drosophila melanogaster. Of the other divalent cations examined, Sr2+, Ni2+, Cu2+, Zn2+ and Hg2+, only Hg2+ failed to cause an increase in Q(+)tRNATyr. For these results, all pre-adult stages of the organism were spent on media containing the divalent ions. Adult flies that had developed on a normal diet also responded to divalent ions; Hg2+ as well as Cd2+, Sr2+ and Zn2+ caused an increase in Q(+)tRNATyr in 4 days. Using adult flies, the rate of the response was measured; when placed on a Cd2+-containing diet, they formed significantly more Q(+)tRNATyr within 24 h as compared to adults on a normal diet. Whether the queuine is derived from the diet or from de novo synthesis is yet to be determined. Since the metal ions represent a range of values in the 'hard-soft' classification, different sites of reaction are expected, yet for Drosophila a common result is an alteration in the ratio of Q(+) and Q(-) isoacceptors of these tRNAs. The transition to Q(+)tRNA may be an early indication of the metabolic imbalances resulting from the presence of the divalent cation.