Fig. 1. (A) A schematic representation of the intronic and exonic elements that affect the splicing of CFTR exon 9: the (TG)m and (T)n polymorphic regions in IVS8, the intronic splicing silencer (ISS) in IVS9, and the exonic enhancer (E) and silencer (S) sequences. (B) A schematic representation of the plasmids used: wild type (11ug/7u) and mutants selectively deleted of the (TG)m and/or (T)n repeats (Δug/Δu), (11ug/Δu) and (Δug/7u). (C) A UV cross-linking assay using HeLa nuclear extract with uniformly labeled RNA of all four constructs linearized with HindIII. The arrows indicate the position of the 50–52 kDa complex.