Expression of exon 2′/2 under the control of CMV or its native promoter. (A) Minigene constructs under the control of a CMV promoter, containing exon 1 and its respective 200, 300, and 400 bp of downstream intronic sequences joined with exon 2′/2 and an equal length of its upstream intronic sequences. (B) Exon 2′ splicing patterns in minigene-transiently transfected or nontransfected MELC. Splicing products were analyzed for exon 2′ inclusion by RT-PCR by the use of a vector-specific primer for minigene or exon 2-specific primer for endogenous 4.1R. (Top panels) RT-PCR products. (Bottom panels) Southern blot with exon 2′ probe (Ex2′). Endo indicates MELC endogenous exon 2′/2 splicing pattern. (C) Exon 2′ splicing patterns in MELC transfected with minigene constructs under the control of their native promoters. RNAs were analyzed from either transiently (T) or stably (S) transfected MELCs. MELCs stably transfected with the respective minigenes under the control of CMV promoters (pCMV) or endogenous (endo) RNAs served as controls. (Top panels) RT-PCR products. (Middle panel) Southern blot with exon 2′ probe (Ex2′). (Bottom panels) Southern blot with exon 2 probe (Ex2). For each construct, 4 transfections were performed per experiment. Each experiment was repeated at least 3 times. Standard deviations are omitted in results that consistently have 0% or 100% of the same product in all 4 reproducible experiments.