A molecular analysis of transformer, a gene in Drosophila melanogaster that controls female sexual differentiation.

The transformer (tra) gene regulates all aspects of somatic sexual differentiation in Drosophila melanogaster females and has no function in males. We have isolated the tra gene as part of a 200 kb chromosomal walk. The 25 kb region around tra contains four genetically identified complementation groups and at least six transcriptional units. Germ-line transformation experiments indicate that a fragment of 2 kb is sufficient to supply tra+ function. Mapping of cDNAs from tra and from the adjacent genes indicates that the tra+ transcription unit is 1.2 kb or less. This transcription unit gives rise to a 1.0 kb RNA that is female-specific and a 1.2 kb RNA that is present in both sexes. tra+ and the gene at the 3' side overlap slightly in the 3' ends of their RNA coding sequences. These results suggest that tra+ function is regulated at the level of production of the female-specific tra RNA. The fact that a tra transcript is found in males raises interesting possibilities for how tra expression is controlled.