Fig. 4. In vitro splicing of the dsx–exon 6D substrates in HeLa S100 extracts complemented with SR proteins. The radiolabeled pre-RNA substrates indicated were spliced in in vitro splicing reaction mixtures containing HeLa S100 extract. Normalized amounts (∼200 ng) of each SR protein preparation were added to the splicing mixture as 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.