FIGURE 4.

Internal deletions that remove PTB binding sites activate splicing. (A) [³²P]-labeled probes were spliced in 30% HeLa nuclear extract for 1, 2, or 3 h and the RNA species resolved by 12% PAGE. T indicates transcript alone. Positions of splicing products and intermediates are indicated to the right. (B) Splicing reactions were incubated for 25 min prior to UV cross-linking and RNase treatment; proteins were resolved by SDS-PAGE. Values below each set of lanes represent the percentage of splicing at 3 h (mean ± SD, n = 4).