Multiple portions of a small region of the Drosophila transformer gene are required for efficient in vivo sex-specific regulated RNA splicing and in vitro sex-lethal binding.

The transformer gene of Drosophila is regulated by Sex-lethal-dependent 3' splice site blockage. 40 nucleotides immediately upstream of the regulated splice site are sufficient to direct sex-specific regulated splicing in transgenic animals. This entire region appears to be necessary for regulation and for efficient Sex-lethal binding. Natural splice sites containing partial homology to transformer do not show regulation. Mutations which replace the 16 nucleotides surrounding the branch point or alter single nucleotides near the splice site eliminate or reduce regulation without eliminating splicing. Mutations which reduce or eliminate regulation in vivo reduce binding to Sex-lethal in vitro, consistent with the hypothesis that these mutations bring about their effects by altering Sex-lethal binding rather than by altering binding sites for additional non-Sex-lethal factors.