Mechanism of suppression inDrosophila melanogasterVIII. Comparison ofsu(s) alleles for ability to suppress the mutants purple, vermilion, and speck

Abstract

SUMMARYThe suppressor of sable [su(s)2] restores the function of vermilion (v), purple (pr) and speck (sp) as well as sable (s) inDrosophila melanogaster. In this report various alleles ofsu(s) are compared for their relative effectiveness on three target mutations,v,prandsp. Three criteria for suppression ofprandvwere employed: visible phenotype, eye pigment levels (drosopterins and xanthommatin) and enzyme levels (sepiapterin synthase and tryptophan oxygenase). Forsponly the visible phenotype was examined. By all three criteriaprwas found to be more easily suppressed thanv;vandspwere comparable. By use ofprwith various alleles ofsu(s) either homozygously or in heterozygous combination withsu(s)+, the extent of suppression ofprcan be best demonstrated by observing the levels of sepiapterin synthase; normal levels of drosopterins were found in females when sepiapterin synthase was only 20% of normal. On the other hand, the extent of suppression ofvis best demonstrated by the amount of xanthommatin eye pigment, because even the suppressed vermilion fly has < 10% of wild-type activity of tryptophan oxygenase when 1-day-old flies are examined; in older flies this enzyme can be as high as 50% of wild type. From these results we also demonstrated thatsu(s)2, and other alleles, are not recessive but, in heterozygous combination withsu(s)+, cause marked suppression ofprand slight, but reproducible, suppression ofv. The purple mutation, therefore, is particularly useful for studying the mechanism of suppression as well as for obtaining new mutant alleles ofsu(s).