C-terminal DNA-binding domain of LuxR-like proteins. This domain contains a helix-turn-helix motif and binds DNA. Proteins belonging to this group are response regulators; some act as transcriptional activators, others as transcriptional repressors. Many are active as homodimers. Many are two domain proteins in which the DNA binding property of the C-terminal DNA binding domain is modulated by modifications of the N-terminal domain. For example in the case of Lux R which participates in the regulation of gene expression in response to fluctuations in cell-population density (quorum-sensing), a signaling molecule, the pheromone Acyl HSL (N-acyl derivatives of homoserine lactone), binds to the N-terminal domain and leads to LuxR dimerization. For others phophorylation of the N-terminal domain leads to multimerization, for example Escherichia coli NarL and Sinorhizobium melilot FixJ. NarL controls gene expression of many respiratory-related operons when environmental nitrate or nitrite is present under anerobic conditions. FixJ is involved in the transcriptional activation of nitrogen fixation genes. The group also includes small proteins which lack an N-terminal signaling domain, such as Bacillus subtilis GerE. GerE is dimeric and acts in conjunction with sigmaK as an activator or a repressor modulating the expression of various genes in particular those encoding the spore-coat. These LuxR family regulators may share a similar organization of their target binding sites. For example the LuxR dimer binds the lux box, a 20bp inverted repeat, GerE dimers bind two 12bp consensus sequences in inverted orientation having the central four bases overlap, and the NarL dimer binds two 7bp inverted repeats separated by 2 bp.
Comment:based on the binding of A.tumefaciens TraR, M.tuberculosis DosR, and E.coli NarL to their target binding sites. Many of these LuxR_like proteins are active as dimers, and may share a similar organization of these target binding sites.
Structure:1ZLK, Mycobacterium tuberculosis DosR C-terminal domain dimer, bound with DNA, contacts at 3.5A.
Structure:1JE8, Escherichia coli NarL dimer, bound with a 20-nucleotide DNA containing a palindromic tail-to-tail arrangement of the nirB -74 promotor site, contacts at 3.5A.
Jiyao W et al.(2023). "The conserved domain database in 2023.",