7.

The 7/8 enhancer directly interacts with the CFTR promoter. Chromosome conformation analysis of CFTR+ Caco2 (A), CFTR+ 16HBE14o- (B) and CFTR- primary skin fibroblasts (C) show higher interaction of the first intron with the promoter in cells with the intron 1 DHS. Cross-linked chro-matin from each cell type was digested with Hind III (sites indicated by dashed lines) and re-ligated. The interaction frequency between a fixed Hind III fragment at the CFTR promoter and Hind III fragments 5′ and within the first, third and seventh introns was measured by Taqman® quantitative PCR. Each reaction was normalized to a control region in the ERCC3gene, as previously described [31]. The amplification efficiencies of all primer sets were verified using Hind III-digested CFTR and ERCC3 BACs. Each experiment was repeated at least twice; a single representative experiment is shown with PCR reactions performed in triplicate. Error bars represent standard error of the mean (n= 3).