A doubtful relationship between tyrosine tRNA and suppression of the vermilion mutant in Drosophila.

The conditions under which Drosophila melanogaster are grown markedly influence the amount of the hypermodified nucleoside Q found in certain tRNAs. This effect on Q biosynthesis was found in both the wild-type and the suppressor of sable [su(s)2] mutant. Suppressed vermilion flies [su(s)2v; bw] with 78% of the tyrosine tRNA in the Q-lacking (gamma) form had brown eyes indistinguishible from su(s)2v; bw flies with only 6% of the tyrosine tRNA in the gamma form. The proposal that this tRNA is a specific inhibitor or tryptophan pyrrolase in vermilion flies, and that its absence in su(s)2 flies is the mechanism of suppression is not consistent with these results. In addition, the su(s)2 locus does not seem to be primarily responsible for controlling Q biosynthesis as previously suggested.