Isolation and characterization of the Beadex locus of Drosophila melanogaster: a putative cis-acting negative regulatory element for the heldup-a gene.

We isolated recombinant lambda phage clones spanning 49 kilobases of DNA which contain the Beadex and heldup-a loci of Drosophila melanogaster. These cloned DNAs were used to analyze the structure of eight dominant mutant alleles of the Beadex locus which show increased gene activity. A region, only 700 base pairs in length, is altered in each of these mutants. Six of the mutations have DNA insertions within this segment. Most of these insertions resemble retrovirus-like transposable elements. In one case (Beadex2) the inserted sequences are homologous to the gypsy transposon family. The other two Beadex alleles were induced by hybrid dysgenesis and suffered deletions which included at least part of the 700-base-pair segment. These deletions appear to have resulted from imprecise excision or deletion of a nearby P element found in the wild-type parental strain. Analysis of one heldup-a allele (heldup-aD30r) indicates that a similar P element-mediated event is responsible for this lesion. In this mutant, deletion of sequences no more than 1,600 base pairs from the Beadex locus accompanies the loss of heldup-a function. The deleted sequences in heldup-aD30r include the entire 700-base-pair segment within which at least part of the Beadex locus resides, yet these flies have no Beadex phenotype. This indicates that a functional heldup-a gene is necessary for expression of the Beadex phenotype. Together, these results suggest that the Beadex functional domain is contained within a short segment of DNA near the heldup-a gene and support the hypothesis that the Beadex locus functions as a cis-acting negative regulatory element for the heldup-a gene.