FIG. 1.

Binding of purified NtcA to wild-type and mutated versions of the ntcA promoter region. EMSA was carried out with a wild-type fragment (A) or with fragments bearing mutations in the proximal (B), distal (C), or both (D) NtcA-binding sites. A scheme of the fragment used in each case, including the positions of TSPs −180, −136, and −49, together with the sequences of wild-type and mutated NtcA-binding sites present in each fragment, is shown in panels A through D. Mutations introduced in each fragment are shown in gray under the wild-type sequence. The positions of free DNA fragments (open triangles), retarded bands (black triangles), and faint bands appearing when a high concentration of NtcA was used (asterisks), as referred to in the text, are indicated. Assay mixtures contained 0.1 fmol of labeled DNA fragment.