A DELETED HOBO ELEMENT IS INVOLVED IN THE UNSTABLE THERMOSENSITIVE VGAL MUTATION AT THE VESTIGIAL LOCUS IN DROSOPHILA-MELANOGASTER

We have described a new unstable mutant of the vestigial locus isolate d from a natural population. From this mutant, vestigial(almost) (vg(a l)), wild-type (vg(al+)), and extreme (vg(ext)), alleles arose spontan eously. The molecular analysis of vg(al) shows that the mutation is du e to a 1874 bp hobo element inserted in a vestigial intron. Two distin ct kinds of events lead a wild-type phenotype. Three independent vg(al +) alleles result from an excision of the hobo element and two other v g(al+) alleles have further deletions of hobo sequence. The sequence o f one of them shows a 1516 bp hobo insertion at the same place and in the same orientation as the 1874 bp insertion. In the vg(ext) alleles, we found a 5' or 3' variably sized deletion of vg sequences. One of t hem, which has been cloned and sequenced, has a deletion finishing exa ctly at the left terminal repeat' hobo element. The genetic implicatio ns of these different genetic structures are discussed.