FIGURE 4.

XylR-NtrC family. (A) Activation mechanism. NtrC effector produces NtrC hexamerization to an ATPase active form, in a way that allows NtrC to make specific contacts with the σ⁵⁴-RNApol holoenzyme and thus remodeling the transcription complex from its closed configuration into an open transcriptionally active form. Activation requires the formation of a DNA loop, aided by IHF. (B) NtrC structure. The crystal structure of the inactive dimer of NtrC1 (1NY5, Lee et al., 2003) is shown. DBD, EDB and AAA⁺ domains as well as the alpha helix that connects EDB with AAA⁺ are highlighted.