A splicing enhancer complex controls alternative splicing of doublesex pre-mRNA.

Female-specific splicing of Drosophila doublesex (dsx) pre-mRNA is regulated by the products of the transformer (tra) and transformer 2 (tra2) genes. In this paper we show that Tra and Tra2 act by recruiting general splicing factors to a regulatory element located downstream of a female-specific 3' splice site. Remarkably, Tra, Tra2, and members of the serine/arginine-rich (SR) family of general splicing factors are sufficient to commit dsx pre-mRNA to female-specific splicing, and individual SR proteins differ significantly in their ability to participate in commitment complex formation. Characterization of the proteins associated with affinity-purified complex formed on dsx pre-mRNA reveals the presence of Tra, Tra2, SR proteins, and additional unidentified components. We conclude that Tra, Tra2, and SR proteins are essential components of a splicing enhancer complex.