Kinetic analysis of operator binding by the E. coli methionine repressor highlights the role(s) of electrostatic interactions

MetJ is a member of the ribbon-helix-helix class of DNA-binding proteins whose affinity for operators is apparently controlled by an unprecedented long-range electrostatic effect from the tertiary sulphur atom of its co-repressor, S-adenosyl methionine. We report here the results of kinetic assays of DNA binding with MetJ mutant proteins having altered net charges. The results (a) suggest that MetJ locates its operators via a sliding mechanism, (b) support the idea that electrostatic steering is important in the initial DNA binding event and (c) highlight the sensitivity of this system to electrostatic effects.