Figure 4.

In vitro binding of protein complexes to CFTR promoter NFRs. (A) EMSA with probes spanning regions of NFRs 1–4 using nuclear extract from the CFTR-expressing cell types Caco2 and 16HBE14o-. Major complexes are observed with probes for NFR4 (single arrow) and NFR1 (two arrows), while NFRs 2 and 3 show very slight protein complex formation. (B) Specificity of complex formation with 16HBE14o- nuclear extracts shown by EMSAs with unlabeled NFR4 and NFR1 oligonucleotides. These efficiently compete complex formation at 10-, 50- and 100-fold molar excess, while mutant oligos (mutated bases shown in gray) are inefficient competitors up to 100-fold molar excess.