Metalloregulators regulate transcription in response to metal ions. Many studies have provided insights into how transcription is activated upon metal binding by MerR-family metalloregulators. In contrast, how transcription is turned off after activation is unclear. Turning off transcription promptly is important, however, as the cells would not want to continue expressing metal resistance genes and thus waste energy after metal stress is relieved. Using single-molecule fluorescence microscopy, we studied the dynamic interactions of CueR, a Cu+-responsive MerR-family metalloregulator, with DNA in vitro and in living E. coli cells. We discovered that in vitro a CueR molecule coming from solution can directly substitute for a DNA-bound CueR or assist the dissociation of the incumbent CueR. The kinetics of the direct protein substitution and assisted dissociation reactions indicate that these two novel processes can provide efficient pathways to replace a DNA-bound holo-CueR with apo-CueR, thus turning off transcription promptly and facilely. We further show that these novel pathways also operate in living bacterial cells where cells can use protein cellular concentrations to modulate transcription regulation kinetics.

Single-molecule dynamics of metalloregulators in vitro and in vivo

248th National Meeting (2014)

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