Fig. 3. In vitro splicing of the dsx–exon 6D substrates. (A) Schematic representation of the dsx–exon 6D splicing substrates. Dsx exonic sequences: dark boxes; ASLV and exon 6D sequences: light boxes. U-to-C, U-to-G, U-to-A and PPE mutations are indicated. (B) In vitro splicing reactions. The radiolabeled pre-RNA substrates indicated were spliced in in vitro splicing reaction mixtures containing HeLa cell nuclear extract. Purified HeLa cell SR proteins (200 ng) were added where indicated. After 2 h of incubation at 30°C, the RNAs were recovered and separated on a 6% polyacrylamide–8 M urea gel. RNA precursors and spliced products are indicated by the schematics on the left.