FIGURE 4.

I nsertion of the enhancer elements in the minigene 45 replicates their activity. A, each element was inserted upstream of the proximal 5′ splice site (ss) of the minigene 45 as indicated. The primers used for subsequent RT-PCR analysis are shown. B, transcripts derived from minigene 45 were incubated in HeLa nuclear extracts in in vitro splicing conditions. RT-PCR analysis was done on total RNA. The splicing products are indicated as well as the proximal/distal (prox/dist) ratios. A new product presumably produced by a cryptic splice site is indicated with an asterisk.