Auto-regulating response regulators in E. coli.

About half of the response regulators (RRs) in E. coli are known to auto-regulate; these are included in the table. (RRs that are not known to auto-regulate are: Atoc, BasR, CreB, DcuR, GlrR, NarP, OmpR, RcsB, RstA, UhpA, UvrY, YedW.) The second column of the table indicates the sign of the auto-regulation: + for activation, − for repression, +/− for both. Note, however, that not all TCS systems are well characterized. When the auto-regulation is inferred from expression studies only, so that indirect regulation is not obviously excluded, the column “evidence” contains a single star (*). If the RR has been shown to bind physically to its cis-regulatory region (by gel retardation studies with purified proteins or by footprinting essays), two stars are assigned. The column “nr. binding sites” specifies the number of binding sites found for the RR at its own promoter. Again, these data ought to be interpreted with care because, for instance, a single binding site for a RR acting as a tetramer can be hard to distinguish from two binding sites of a RR acting as a dimer. The table shows that, for RRs, auto-activation is more common than auto-repression, and that it is typically mediated by 1 or 2 binding sites.