Cis-trans tests at the Notch locus of Drosophila melanogaster suggesting multiple cis-acting control sites inside the locus

Abstract

Tests were made of expression of Abruptex in compounds of recessive mutations and dominant antimorphic Abruptex (Ax) mutations at the Notch locus of Drosophila melanogaster. In combination with split, expression of Abruptex was stronger in cis‐heterozygotes than in trans‐heterozygotes, whereas the split homozygotes tended to be intermediate. In combination with facet‐glossy, the expression of Abruptex was stronger in trans‐heterozygotes than in cis‐heterozygotes and the facet‐glossy homozygotes tended to be intermediate. The Abruptex mutations usually have a stronger expression in all combinations with split than with facet‐glossy. Split showed a pseudodominant expression both in cis‐and trans‐heterozygotes but facet glossy only in trans‐heterozygotes. The +Ax++ heterozygotes were most expressed of all genotypes in respect to wing venation, but approximately at the same level as the two trans‐heterozygotes in the bristle phenotype. These results tentatively suggest that the Notch locus can be divided into a structural element consisting of a right‐most fifth of the locus including the site of Abruptex, and a control element apparently including several cis‐acting sites. In cis‐compounds split enhances and facet‐glossy suppresses the expression of the presumed structural element. The homologous chromosome, however, also seems to be affected by these control sites, which suggests that the effect of the cis‐acting control sites would be at the level of transcription.