Transcriptional switches regulate gene expression in response to environmental changes surrounding cell. Many studies have focused on two fundamentally different models of transcriptional control by bacterial metalloregulatory protein. Distortion of the DNA fragment including cis-element, to which the trans-acting factor MerR binds, is accepted as the mechanism of gene expression regulation by Hg (II) while, in cases of the other trans-acting factors ArsR and CadC, events of association to and dissociation from cis-element are known to control transcription in response to As (III) and Cd (II), respectively. In this study, interactions between green-fluorescent-protein-tagged trans-acting factor and immobilized cis-element were analyzed on solid surface. Fluorescent measurements and surface plasmon resonance (SPR) responses revealed that although the equilibrium dissociation constant (KD) was much lower in MerR than in ArsR and CadC, the dissociation rate of MerR from DNA increased in response to Hg (II) at concentrations of 5-10(4) µg l(-1). These results firstly demonstrate an increase of KD between MerR and its recognition site in DNA by Hg (II), and possibility of rapid Hg (II) quantification with the low detection limit (5 µg l(-1)) and the high dynamic range (10(1)-10(4) µg l(-1)).
Keywords: Dissociation constant; Mercury; Metalloregulatory protein; Promoter; SPR.
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