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Abstract
The Drosophila melanogaster doublesex (dsx) pre-mRNA is alternatively spliced in a sex-specific manner. The female-specific pattern of splicing results from the activation of an otherwise weak 3$\sp\prime$ splice site, and is dependent on the proteins Transformer (Tra) and Transformer-2 (Tra2), and on a cis-acting element, the dsxRE, which contains six copies of a 13-nt repeat sequence. Previous studies have shown that Tra and Tra2 bind to the dsxRE along with several members of the SR family of general splicing factors to form a splicing enhancer complex (dsxEC). In this thesis I describe the characterization of several additional sequence elements located within, or flanking, the dsxRE, and show that at least one of these elements, the PRE, is required along with the repeat sequences for optimal activation of the female-specific 3$\sp\prime$ splice site. In addition I have identified the SR proteins which are specifically recruited by Tra and Tra2 to the dsxRE, and have determined that distinct SR/Tra/Tra2 heterotrimeric complexes associate with both the repeat sequences and the PRE. Therefore, I conclude that the dsxEC is formed through multiple, cooperative protein-protein and protein-RNA interactions. A comparison of the regulation of dsx pre-mRNA with other known examples of regulated splicing indicates that the interactions which comprise the dsxEC may provide a general model for how multiple factors can cooperate to mediate the activation of splicing.
