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5  structures 18084  species 0  interactions 78301  sequences 133  architectures

Family: MerR_1 (PF13411)

Summary: MerR HTH family regulatory protein

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MerR HTH family regulatory protein Provide feedback

No Pfam abstract.

Internal database links

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR000551

The merR-type HTH domain is a DNA-binding, winged helix-turn-helix (wHTH) domain of about 70 residues present in the merR family of transcriptional regulators [PUBMED:2492496]. MerR-type regulators are present in diverse bacterial genera, in the cytoplasm. The helix-turn-helix DNA-binding motif is located in the N-terminal part of these transcriptional regulators and is followed by a coiled-coil region. The C-terminal part of merR-type regulators contains effector binding regions that are specific to the effector recognised. Most merR-type transcriptional regulators respond to environmental stimuli, like heavy metals, oxidative stress or antibiotics and a subgroup of metalloregulators are bacterial transcription activators that respond to metal ions [PUBMED:12829265].

Several structures of merR-type transcriptional regulators have been resolved and their N-terminal DNA-binding domains are ascribed to the superfamily of winged-helix proteins, containing a four-helix (H) bundle and a three-stranded antiparallel beta-sheet (B) in the topology: B1-H1-H2-B2-B3-H3-H4 [PUBMED:12186881]. The helix-turn-helix motif comprises the first and second helices, the second being called the recognition helix. The HTH is involved in DNA-binding into the major groove, where the recognition helix makes most DNA-contacts. The second DNA-binding element is wing W1, composed of the second and third beta-strands and their connecting loop. The third DNA-binding element, wing W2, is not a loop like in typical winged-helix proteins, but another H-T-H motif formed by helices three and four. In a typical merR regulator, the HTH and two wings bind the promoter of the regulated operon between the -35 and -10 regions in a spacer of 19/20 bp and longer than usual, distorting the operator DNA and causing RNA polymerase to initiate transcription [PUBMED:12829265]. Most merR-like transcriptional regulators are dimers.

Some proteins known to contain a merR-type HTH domain:

  • Tn501 merR, mercuric resistance operon regulatory protein. 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.
  • Bacillus subtilis bltR, bmrR and mtaN (ywnD), transcriptional activators of the blr and bmr transporters involved in multidrug resistance.
  • Escherichia coli soxR, responds to oxidative stress and autoregulatory controls a superoxide response regulon.
  • Bradyrhizobium japonicum nolA, a transcriptional regulator involved in the genotype-specific nodulation of soybeans.
  • Streptomyces lividans tipA, a transcriptional activator which binds to and is activated by the antibiotic thiostrepton.
  • Escherichia coli zntR, a zinc-responsive regulator of zntA ATPase.
  • Escherichia coli cueR , a regulator of the copper efflux regulon.
  • CarA (Q1DDV9) and CarH (Q1DDV8) from Myxococcus xanthus, paralogous repressors that requires B(12) to down-regulation of a light-inducible promoter [PUBMED:21502508, PUBMED:18315685].
  • TtCarH (Q746J7) from Thermus thermophilus, belongs to a class of photoreceptors that use 5'-deoxyadenosylcobalamin (AdoB12) as the light-sensing chromophore [PUBMED:23512413].

Gene Ontology

The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.

Domain organisation

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Pfam Clan

This family is a member of clan HTH (CL0123), which has the following description:

This family contains a diverse range of mostly DNA-binding domains that contain a helix-turn-helix motif.

The clan contains the following 217 members:

AphA_like Arg_repressor ARID B-block_TFIIIC Bac_DnaA_C BetR Bot1p BrkDBD CENP-B_N Cro Crp CSN8_PSD8_EIF3K DDRGK Dimerisation Dimerisation2 DsrD DUF1133 DUF1153 DUF1323 DUF134 DUF1441 DUF1492 DUF1495 DUF1670 DUF1804 DUF1836 DUF1870 DUF2089 DUF2250 DUF2316 DUF2582 DUF3116 DUF3853 DUF387 DUF3908 DUF4364 DUF739 DUF742 DUF977 E2F_TDP Ets Exc F-112 FaeA Fe_dep_repr_C Fe_dep_repress FeoC Ftsk_gamma FUR GcrA GerE GntR HARE-HTH HemN_C Homeobox Homeobox_KN Homez HrcA_DNA-bdg HSF_DNA-bind HTH_1 HTH_10 HTH_11 HTH_12 HTH_13 HTH_15 HTH_16 HTH_17 HTH_18 HTH_19 HTH_20 HTH_21 HTH_22 HTH_23 HTH_24 HTH_25 HTH_26 HTH_27 HTH_28 HTH_29 HTH_3 HTH_30 HTH_31 HTH_32 HTH_33 HTH_34 HTH_35 HTH_36 HTH_37 HTH_38 HTH_39 HTH_40 HTH_41 HTH_42 HTH_43 HTH_45 HTH_46 HTH_47 HTH_5 HTH_6 HTH_7 HTH_8 HTH_9 HTH_AraC HTH_AsnC-type HTH_CodY HTH_Crp_2 HTH_DeoR HTH_IclR HTH_Mga HTH_micro HTH_OrfB_IS605 HTH_psq HTH_Tnp_1 HTH_Tnp_1_2 HTH_Tnp_4 HTH_Tnp_IS1 HTH_Tnp_IS630 HTH_Tnp_ISL3 HTH_Tnp_Mu_1 HTH_Tnp_Mu_2 HTH_Tnp_Tc3_1 HTH_Tnp_Tc3_2 HTH_Tnp_Tc5 HTH_WhiA HxlR IF2_N KORA KorB LacI LexA_DNA_bind LZ_Tnp_IS481 MADF_DNA_bdg MarR MarR_2 MerR MerR-DNA-bind MerR_1 MerR_2 Mga Mnd1 Mor MotA_activ MqsA_antitoxin MRP-L20 Myb_DNA-bind_2 Myb_DNA-bind_3 Myb_DNA-bind_4 Myb_DNA-bind_5 Myb_DNA-bind_6 Myb_DNA-bind_7 Myb_DNA-binding Neugrin NUMOD1 OST-HTH P22_Cro PaaX PadR PAX PCI Penicillinase_R Phage_AlpA Phage_antitermQ Phage_CI_repr Phage_CII Phage_rep_org_N Phage_terminase Pou Pox_D5 PuR_N Put_DNA-bind_N Rap1-DNA-bind Rep_3 RepA_C RepA_N RepC RepL Replic_Relax RFX_DNA_binding Ribosomal_S19e Ribosomal_S25 Rio2_N RNA_pol_Rpc34 RP-C RPA RPA_C RQC Rrf2 RTP RuvB_C SAC3_GANP SANT_DAMP1_like SatD SgrR_N Sigma54_CBD Sigma54_DBD Sigma70_ECF Sigma70_r2 Sigma70_r3 Sigma70_r4 Sigma70_r4_2 SLIDE SpoIIID Sulfolobus_pRN TBPIP Terminase_5 TetR_N TFIIE_alpha Tn916-Xis TraI_2_C Trans_reg_C TrfA TrmB Trp_repressor UPF0122 YdaS_antitoxin YokU z-alpha


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Seed source: Jackhmmer:C2D3E8
Previous IDs: none
Type: Family
Author: Coggill P
Number in seed: 137
Number in full: 78301
Average length of the domain: 69.30 aa
Average identity of full alignment: 28 %
Average coverage of the sequence by the domain: 36.16 %

HMM information View help on HMM parameters

HMM build commands:
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 80369284 -E 1000 --cpu 4 HMM pfamseq
Model details:
Parameter Sequence Domain
Gathering cut-off 21.6 21.6
Trusted cut-off 21.6 21.6
Noise cut-off 21.5 21.5
Model length: 69
Family (HMM) version: 2
Download: download the raw HMM for this family

Species distribution

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Archea Archea Eukaryota Eukaryota
Bacteria Bacteria Other sequences Other sequences
Viruses Viruses Unclassified Unclassified
Viroids Viroids Unclassified sequence Unclassified sequence


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For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the MerR_1 domain has been found. There are 5 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.

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