Mechanism of suppression in Drosophila: a change in tyrosine transfer RNA.

Abstract

The mechanism of suppression of the vermilion locus in Drosophila melanogaster is examined. The suppressor locus, su(s)2, is shown to control directly the amount of a specific tyrosine transfer RNA which occurs in the adult fly. Wild-type flies have three chromatographic forms of tyrosine tRNA but flies that are homozygous for the suppressor gene su(s)2 contain little or none of the second chromatographic form. The isoacceptor patterns of tRNA for leucine, phenylalanine and serine are identical in the suppressor mutant and wild-type fly. Genetic data show that the phenotypic expression of su(s)2 and the altered chromatographic pattern of tyrosine tRNA are recessive and that both map at the same position on the left tip of the X chromosome. Furthermore, another suppressor of vermilion was induced by ethyl methane sulfate, su(s)e1, that is at the same locus as su(s)2 and that produces the same change in tyrosine tRNA as su(s)2. The recessive character of the suppressor mutants is evident both in the phenotypic expression and in the alteration of the tyrosine tRNA. This recessive character indicates that the suppressor locus is not the locus for the primary structure of tyrosine tRNA but that it may control an enzyme that modifies the tyrosine tRNA in some way.