A NEW FAMILY OF GENES WHICH, WHEN MUTATED, SUPPRESS THE INHIBITORY EFFECT OF THE MOD(MDG4)(1U1) MUTATION ON Y(2) EXPRESSION IN DROSOPHILA-MELANOGASTER

The suppressor of Hairy-wing [su(Hw)] protein inhibits the function of transcriptional enhancers located distal to the promoter with respect to the location of su(Hw)-binding sites (insulation). Mutations in th e modifier of mdg4 [mod(mdg4)] interfere with insulation and enhance t he effect of the su(Hw)-binding region inserted in the y(2) mutation b y inhibiting the function of regulatory elements located on both sides of the su(Hw)-binding region. From P-M hybrid dysgenic crosses, 21 mu tations that suppress the negative effect of the mod(mdg4)(1u1) mutati on on the y(2) allele were obtained among 47000 flies scored. These Su (mg) mutations have a dominant suppressor effect and map to at least 1 3 different loci. Some of Su(mg) mutations also suppress the effect of mod(mdg4)(1u1) on two other gypsy-induced mutations, sc(D1) and ct(6) . Most of Su(mg) mutations do not affect the viability or fertility of homozygous flies. We speculate that the Su(mg) genes represent a new family of redundant regulatory genes in Drosophila melanogaster.