The MerR family of transcriptional regulators

The MerR family is a group of transcriptional activators with similar N‐terminal helix‐turn‐helix DNA binding regions and C‐terminal effector binding regions that are specific to the effector recognised. The signature of the family is amino acid similarity in the first 100 amino acids, including a helix‐turn‐helix motif followed by a coiled‐coil region. With increasing recognition of members of this class over the last decade, particularly with the advent of rapid bacterial genome sequencing, MerR‐like regulators have been found in a wide range of bacterial genera, but not yet in archaea or eukaryotes. The few MerR‐like regulators that have been studied experimentally have been shown to activate suboptimal σ 70 ‐dependent promoters, in which the spacing between the −35 and −10 elements recognised by the σ factor is greater than the optimal 17±1 bp. Activation of transcription is through protein‐dependent DNA distortion. The majority of regulators in the family respond to environmental stimuli, such as oxidative stress, heavy metals or antibiotics. A subgroup of the family activates transcription in response to metal ions. This subgroup shows sequence similarity in the C‐terminal effector binding region as well as in the N‐terminal region, but it is not yet clear how metal discrimination occurs. This subgroup of MerR family regulators includes MerR itself and may have evolved to generate a variety of specific metal‐responsive regulators by fine‐tuning the sites of metal recognition.