Excess function hairy-wing mutations caused by gypsy and copia insertions within structural genes of the achaete-scute locus of Drosophila.

Hairy-wing (Hw) mutations cause the differentiation of extra chaetes on the cuticle of Drosophila. They are associated with modifications of the achaete-scute complex that consist, in the mutants studied, of insertions of the transposable elements gypsy (Hw1, HwBS) or copia (HwUa). gypsy and copia are inserted in achaete and scute transcribed regions, respectively. Transcription of the insertion-split genes starts at the normal site but terminates within the transposable element sequences. The RNA truncated within gypsy is 5-20 times more abundant than its homolog in wild-type flies. The abundance is reduced in Hw1 revertants and Hw1 stocks carrying su(Hw) mutations. These and other data suggest that the excess function phenotypes of Hw mutations are generated by an increase in achaete or scute transcripts.