Genetic identification of dominant overproducing mutations: the Beadex gene.

A model system for the identification of presumptive overproducing mutations from among visible dominant mutations in D. melanogaster is described. An overproducing mutation is expected if a dominant mutation is readily reverted by gene deletion and if gene deletions suppress the expression of the original dominant mutation in flies heterozygous for the deletion. The Beadex (1:59.4) mutations are shown to satisfy these requirements, since a Bx dominant mutations is reverted by induced deletion [Df(Bx)/+) is wild type], and is also suppressed in trans by such a deletion [(Bx/Df)Bx) is wild type]. In addition, all 13 mutations recovered as Bx reversions or suppressors were associated with recessive held up (hdp) mutations allelic inter se, but not allelic to any known hdp gene. One such hdp mutations does not function as an independent dominant suppressor of Bx, is not always associated with Bx deletion, and in the latter situation is readily separable from Bx. We suggest that it functions as a Bx deletion, and may therefore represent the structural gene which is cis-regulated by the overproducing Bx mutations.