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78  structures 5450  species 2  interactions 49289  sequences 88  architectures

Family: LacI (PF00356)

Summary: Bacterial regulatory proteins, lacI family

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Bacterial regulatory proteins, lacI family Provide feedback

No Pfam abstract.

Internal database links

External database links

This tab holds annotation information from the InterPro database.

InterPro entry IPR000843

The lacI-type HTH domain is a DNA-binding, helix-turn-helix (HTH) domain of about 50-60 residues present in the lacI/galR family of transcriptional regulators involved in metabolic regulation in prokaryotes. Most of these bacterial regulators recognize sugar-inducers. The family is named after the Escherichia coli lactose operon repressor lacI and galactose operon repressor galR. LacI-type regulators are present in diverse bacterial genera, in the cytoplasm. The 'helix-turn-helix' DNA-binding motif is located in the N-terminal extremity of these transcriptional regulators. The C-terminal part of lacI-type regulators contains several regions that can be involved in (1) binding of inducers, which are sugars and their analogues and (2) oligomerization. The lac repressor is a tetramer, whilst the gal and cyt repressors are dimers. LacI-type transcriptional regulators are important in the coordination of catabolic, metabolic and transport operons [PUBMED:1805309, PUBMED:1639817].

Several structures of lacI-type transcriptional regulators have been resolved and their DNA-binding domain encompasses a headpiece, formed by a fold of three helices, followed by a hinge region, which can form a fourth alpha helix or hinge-helix. 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, while the hinge-helix fits into the minor groove and the complete domain specifically recognizes the operator DNA [PUBMED:8543068].

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

  • Bacillus subtilis ccpA and ccpB, transcriptional regulators involved in the catabolic repression of several operons.
  • Salmonella typhimurium fruR, the fructose repressor, involved in the regulation of a large number of operons encoding enzymes which take part in central pathways of carbon metabolism.
  • Escherichia coli lacI, the lactose operon repressor, serving as a model for gene regulation.
  • Escherichia coli purF and purR, repressors involved in the regulation of enzymes for purine nucleotide synthesis.
  • Haemophilus influenzae galR, a repressor of the galactose operon.

Gene Ontology

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

Domain organisation

Below is a listing of the unique domain organisations or architectures in which this domain is found. More...

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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 340 members:

AbiEi_3_N AbiEi_4 ANAPC2 AphA_like Arg_repressor ARID ArsR B-block_TFIIIC B5 Bac_DnaA_C Baculo_PEP_N BetR BHD_3 BLACT_WH Bot1p BrkDBD BsuBI_PstI_RE_N C_LFY_FLO CaiF_GrlA CarD_CdnL_TRCF CDC27 Cdc6_C Cdh1_DBD_1 CDT1 CDT1_C CENP-B_N Costars CPSase_L_D3 Cro Crp CSN4_RPN5_eIF3a CSN8_PSD8_EIF3K CtsR Cullin_Nedd8 CUT CUTL