Figure 2.

Activities of domain-swap proteins in a splicing commitment assay. (A) Human β-globin pre-mRNA (transcribed from a minigene, pSP73–HβΔ6, which comprises exons G1 and G2 and intron 1) was spliced in the absence (lane 1) or the presence (lanes 2–9) of unlabeled competitor RNA corresponding to the 5′ half of the human β-globin pre-mRNA (4, 25). In each lane (from 2 to 9), 0.2 μg of the indicated protein was preincubated with the labeled pre-mRNA, followed by the addition of 3 μl of HeLa cell nuclear extract blocked with 2 pmol of unlabeled competitor RNA. (B) HIV tat pre-mRNA (transcribed from a minigene, pSP73-tat, which contains exons T2 and T3 and a truncated intron 1) was spliced under the same conditions. The bands corresponding to splicing intermediates and products are indicated. ∗, aberrant tat pre-mRNA cleavage product unrelated to splicing as previously described (11). Splicing efficiency is shown as the ratio of spliced to unspliced RNA underneath each lane.