FIG. 4.

Functional characterization of SC35-dependent enhancers. (A) The dsx pre-mRNA substrates are indicated schematically, with the dsx portion shown in black. Sequences of the different splicing enhancers tested are in capital letters; sequences common to all dsx-N18 clones are in lowercase letters. The dsx-PRE construct is similar but not identical to the dsx-N18 constructs, as it does not contain an inert Sa element. (B) Two dsx-N18 clones that show sequence homology are specifically activated by SC35. The pre-mRNA used in the S100 complementation reactions is indicated above the autoradiogram. The presence of the indicated reaction component in splicing assays and complementation reactions is indicated by a plus sign above the appropriate reaction lane: HeLa cell nuclear extract (NE), HeLa S100 extract complemented with buffer D (S100), or the SR protein indicated by a plus sign. Amounts of SC35 and SF2/ASF used in the complementation assays were 400 and 200 ng, respectively. The dsx-N18 and dsx-PRE pre-mRNAs and spliced products are resolved on a 10% denaturing polyacrylamide gel; their positions are indicated to the right.