Three novel sequence variations in the 5' upstream region of the cystic fibrosis transmembrane conductance regulator (CFTR) gene: two polymorphisms and one putative molecular defect.

More than 400 sequence alterations have been identified in the whole coding sequence of the cystic fibrosis transmembrane conductance regulator (CFTR) gene corresponding to the 27 exons and their exon-intron boundaries. However, in some CF chromosomes, no mutation has yet been detected. In such cases, we have explored the promoter and the sequence up to position -1000 from the cap site, by using denaturing gradient gel electrophoresis. This study concerning 35 CF chromosomes has allowed us to identify three novel sequence variations located in the 5' upstream region of the gene. The T to G substitution located at position -895 from the cap site could be considered as a polymorphic variation. The second substitution (C to T at position -816) has been detected on only one CF chromosome, but does not concern a regulatory DNA element previously described. Conversely, the third substitution (a T to G substitution at position -741 from the cap site) is located at a potential AP-1 binding site. We have investigated, by electrophoretic mobility shift assay, the ability of this region to bind nuclear factors. We have found that the normal sequence between -740/-745 does not bind either the AP-1 transcription factor or AP-1 related proteins, and that the T to G-741 mutated sequence exhibits an abnormal binding pattern suggesting the possible deleterious effect of still unknown negative trans-acting factors.