FIG. 7.

The ACE resembles sequences in the dsx and fru splicing enhancers, and its deletion reduces Tra2 binding. (A) Schematic showing the sequence and location of the tra2 ACE (striped box) and its relationship to the repeated enhancer elements found in dsx and fru RNA. The five CAAC repeats are underlined with arrows. Top arrows, sites in the 13-nt dsx repeat sequence of site-specific cross-linking to Tra2. (B) UV cross-linking was performed on the 188-nt dsx ESE fragment in the presence of splicing-competent Drosophila nuclear extract, 3 pmol of recombinant Tra2, and increasing amounts of RNA competitors (0.5, 2.5, and 12.5 pmol). The position of RNA 2 is shown in Fig. 3A. RNA 2 ΔACE contains a precise deletion of the 34-nt ACE but is otherwise identical. Rbp1 binding to the dsx ESE is dependent on Tra2 binding (Fig. 3B) and is reduced when Tra2 is competed (lane 3). Note that, although RNA 2 competition affects Tra2 and Rbp1, other cross-linking bands are unaffected. wt, wild type.