| Primary Identifier | IPR000843 | Type | Domain |
| Short Name | HTH_LacI |
| description | The lacI-type HTH domain is a DNA-binding, helix-turn-helix (HTH) domain ofabout 50-60 residues present in the lacI/galR family of transcriptionalregulators involved in metabolic regulation in prokaryotes. Most of thesebacterial regulators recognize sugar-inducers. The family is named after theEscherichia coli lactose operon repressor lacI and galactose operon repressorgalR. LacI-type regulators are present in diverse bacterial genera, in thecytoplasm. The 'helix-turn-helix' DNA-binding motif is located in theN-terminal extremity of these transcriptional regulators. The C-terminal partof 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 cytrepressors are dimers. LacI-type transcriptional regulators are important inthe coordination of catabolic, metabolic and transport operons [, ].Several structures of lacI-type transcriptional regulators have been resolvedand their DNA-binding domain encompasses a headpiece, formed by a fold ofthree helices, followed by a hinge region, which can form a fourth α-helixor hinge-helix. The helix-turn-helix motif comprises thefirst and second helices, the second being called the recognition helix. TheHTH is involved in DNA-binding into the major groove, while the hinge-helixfits into the minor groove and the complete domain specifically recognizes theoperator DNA [].Some proteins known to contain a lacI-type HTH domain:Bacillus subtilis ccpA and ccpB, transcriptional regulators involved inthe catabolic repression of several operons.Salmonella typhimurium fruR, the fructose repressor, involved in theregulation of a large number of operons encoding enzymes which take part incentral pathways of carbon metabolism.Escherichia coli lacI, the lactose operon repressor, serving as a model forgene regulation.Escherichia coli purF and purR, repressors involved in the regulation ofenzymes for purine nucleotide synthesis.Haemophilus influenzae galR, a repressor of the galactose operon. |
