FIGURE 12.

Sequence of events for OmpR activation and DNA binding. Step1, OmpR binds as a monomer to the high affinity C1b site located 3′ to its upstream half-site C1a. Step 2, conformational change occurs in the N-terminal receiver domain as a consequence of the C terminus binding to DNA. This promotes phosphorylation of Asp⁵⁵ in the receiver domain. Step 3, as a consequence of phosphorylation, the receiver domains form symmetric dimers. Step 4, dimerization brings the second OmpR_C domain to its lower affinity site, promoting DNA binding by the second OmpR_C. If the orientation of C1b is reversed, the dimer still forms, presumably because the longer, more flexible linker enables OmpR_C to bind.