Members of the IclR family of bacterial transcriptional regulators function as activators and/or repressors

• Published in: FEMS microbiology reviews Vol. 30; no. 2; pp. 157 - 186
• Main Authors: Molina-Henares, Antonio J., Krell, Tino, Eugenia Guazzaroni, Maria, Segura, Ana, Ramos, Juan L.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-03-2006; Blackwell Science Ltd; Oxford University Press
• Subjects: Amino Acid Sequence; Aromatic compounds; Bacterial Proteins - chemistry; Bacterial Proteins - physiology; Binding sites; Biodegradation; catabolic pathways; Cyclic AMP Receptor Protein - physiology; Databases, Genetic; Deactivation; Deoxyribonucleic acid; Dimers; DNA; DNA-directed RNA polymerase; Erwinia - pathogenicity; Escherichia coli Proteins - chemistry; Escherichia coli Proteins - genetics; Escherichia coli Proteins - physiology; Gene Expression Regulation, Bacterial - genetics; Glyoxylates - metabolism; Helix-Turn-Helix Motifs - genetics; IclR family; Inactivation; Krebs cycle control; Molecular Sequence Data; Multidrug resistance; Pathogenicity; Pathogens; profiles; Protein Structure, Secondary; Protein Structure, Tertiary; Proteins; Regulators; Repressor Proteins - chemistry; Repressor Proteins - genetics; Repressor Proteins - physiology; Repressors; Ribonucleic acid; RNA; RNA polymerase; Sequence Homology, Amino Acid; Shunt resistance; solvent efflux pumps; Sporulation; Streptomyces - genetics; Streptomyces - physiology; Thermotoga maritima - genetics; Transcription; Transcription Factors - chemistry; Transcription Factors - genetics; Transcription Factors - physiology; IclR family; profiles; solvent efflux pumps; Krebs cycle control; catabolic pathways; sporulation
• ISSN: 0168-6445; 1574-6976; 1574-6976
• DOI: 10.1111/j.1574-6976.2005.00008.x

Abstract
Members of the IclR family of regulators are proteins with around 250 residues. The IclR family is best defined by a profile covering the effector binding domain. This is supported by structural data and by a number of mutants showing that effector specificity lies within a pocket in the C-terminal domain. These regulators have a helix-turn-helix DNA binding motif in the N-terminal domain and bind target promoters as dimers or as a dimer of dimers. This family comprises regulators acting as repressors, activators and proteins with a dual role. Members of the IclR family control genes whose products are involved in the glyoxylate shunt in
Enterobacteriaceae
, multidrug resistance, degradation of aromatics, inactivation of quorum-sensing signals, determinants of plant pathogenicity and sporulation. No clear consensus exists on the architecture of DNA binding sites for IclR activators: the MhpR binding site is formed by a 15-bp palindrome, but the binding sites of PcaU and PobR are three perfect 10-bp sequence repetitions forming an inverted and a direct repeat. IclR-type positive regulators bind their promoter DNA in the absence of effector. The mechanism of repression differs among IclR-type regulators. In most of them the binding sites of RNA polymerase and the repressor overlap, so that the repressor occludes RNA polymerase binding. In other cases the repressor binding site is distal to the RNA polymerase, so that the repressor destabilizes the open complex.