The many bacterial transcription regulation proteins which bind DNA through a 'helix-turn-helix' motif can be classified into subfamilies on the basis of sequence similarities. One of these is the MerR subfamily. MerR, which is found in many bacterial species mediates the mercuric-dependent induction of the mercury resistance operon. In the absence of mercury merR represses transcription by binding tightly, as a dimer, to the 'mer' operator region; when mercury is present the dimeric complex binds a single ion and becomes a potent transcriptional activator, while remaining bound to the mer site. Members of the family include the mercuric resistance operon regulatory protein merR; Bacillus subtilis bltR and bmrR; Bacillus glnR; Streptomyces coelicolor hspR; Bradyrhizobium japonicum nolA; Escherichia coli superoxide response regulator soxR; and Streptomyces lividans transcriptional activator tipA [(PUBMED:7688297), (PUBMED:2492496), (PUBMED:7608059), (PUBMED:1677938), (PUBMED:1988958), (PUBMED:2305262)]. Other members include hypothetical proteins from E. coli, B. subtilis and Haemophilus influenzae. Within this family, the HTH motif is situated towards the N terminus.
GO process:
regulation of transcription, DNA-dependent (GO:0006355)
GO function:
sequence-specific DNA binding transcription factor activity (GO:0003700)
Family alignment:
There are 7663
HTH_MERR domains in 7569 proteins in SMART's nrdb database.
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Evolution (species in which this domain is found)
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This tree shows only several representative species. The complete taxonomic breakdown of all proteins with HTH_MERR domain is also avaliable.
The MerR metalloregulatory protein binds mercuric ion as a tricoordinate, metal-bridged dimer.
Science. 1990; 247: 946-8
Display abstract
Bacterial MerR proteins are dimeric DNA-binding proteins that mediate the Hg(II)-dependent induction of mercury resistance operons. Site-directed mutagenesis of the Bacillus sp. RC607 MerR protein reveals that three of four Cys residues per monomer are required for Hg(II) binding at the single high-affinity binding site. Inactive mutant homodimers can exchange subunits to form heterodimers active for Hg(II) binding. Studies of a heterodimer retaining only three of eight cysteine residues per dimer reveal that Cys79 in one subunit and Cys114 and Cys123 in the second subunit are necessary and sufficient for high-affinity Hg(II) binding in an asymmetric, subunit bridging coordination complex.
Metabolism (metabolic pathways involving proteins which contain this domain)
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This information is based on mapping of SMART genomic protein database to KEGG orthologous groups. Percentage points are related to the number of proteins with HTH_MERR domain which could be assigned to a KEGG orthologous group, and not all proteins containing HTH_MERR domain. Please note that proteins can be included in multiple pathways, ie. the numbers above will not always add up to 100%.
to expand nodes. To display all proteins with a HTH_MERR domain in a specific node, click on it.
