BX minigene: mutated splice sites and scores. (a) Scheme of the BX minigene construct. Exons: grey boxes. Introns: horizontal lines. Two lines cutting introns indicate that the whole intron was not cloned. The naturally occurring β-Gal (above the exons) and EBP (below the exons) splicing pathways are indicated. * (in red) indicates the location of the changes introduced by site-directed mutagenesis in BX3 and BX4 constructs. Arrows indicate the location of T7 and SP6 primers. PCMV: CMV promotor; BGHpA: BGH polyadenylation site. (b) 3'ss wild-type and mutated sequences and calculated splicing scores. Changes introduced by mutagenesis are underlined. cons: plasmid construct.