ABSTRACT
The GNTR family of transcription factors (TFs) is a large group of proteins present in diverse bacteria and regulating various biological processes. Here we use the comparative genomics approach to reconstruct regulons and identify binding motifs of regulators from three subfamilies of the GNTR family, FADR, HUTC, and YTRA. Using these data, we attempt to predict DNA-protein contacts by analyzing correlations between binding motifs in DNA and amino acid sequences of TFs. We identify pairs of positions with high correlation between amino acids and nucleotides for FADR, HUTC, and YTRA subfamilies and show that the most predicted DNA-protein interactions are quite similar in all subfamilies and conform well to the experimentally identified contacts formed by FadR from E. coli and AraR from B. subtilis. The most frequent predicted contacts in the analyzed subfamilies are Arg-G, Asn-A, Asp-C. We also analyze the divergon structure and preferred site positions relative to regulated genes in the FADR and HUTC subfamilies. A single site in a divergon usually regulates both operons and is approximately in the middle of the intergenic area. Double sites are either involved in the co-operative regulation of both operons and then are in the center of the intergenic area, or each site in the pair independently regulates its own operon and tends to be near it. We also identify additional candidate TF-binding boxes near palindromic binding sites of TFs from the FADR, HUTC, and YTRA subfamilies, which may play role in the binding of additional TF-subunits.
Subject(s)
Bacterial Proteins/metabolism , DNA, Bacterial/metabolism , DNA-Binding Proteins/metabolism , Transcription Factors/metabolism , Amino Acid Sequence , Bacillus subtilis/genetics , Bacillus subtilis/metabolism , Bacteria/classification , Bacteria/genetics , Bacteria/metabolism , Bacterial Proteins/genetics , Base Sequence , Binding Sites/genetics , DNA, Bacterial/genetics , DNA-Binding Proteins/genetics , Escherichia coli/genetics , Escherichia coli/metabolism , Escherichia coli Proteins/genetics , Escherichia coli Proteins/metabolism , Evolution, Molecular , Genome, Bacterial/genetics , Genomics/methods , Molecular Sequence Data , Nucleotide Motifs/genetics , Operon/genetics , Regulon/genetics , Sequence Homology, Amino Acid , Sequence Homology, Nucleic Acid , Transcription Factors/geneticsABSTRACT
Redox-sensing repressor Rex was previously implicated in the control of anaerobic respiration in response to the cellular NADH/NAD(+) levels in gram-positive bacteria. We utilized the comparative genomics approach to infer candidate Rex-binding DNA motifs and assess the Rex regulon content in 119 genomes from 11 taxonomic groups. Both DNA-binding and NAD-sensing domains are broadly conserved in Rex orthologs identified in the phyla Firmicutes, Thermotogales, Actinobacteria, Chloroflexi, Deinococcus-Thermus, and Proteobacteria. The identified DNA-binding motifs showed significant conservation in these species, with the only exception detected in Clostridia, where the Rex motif deviates in two positions from the generalized consensus, TTGTGAANNNNTTCACAA. Comparative analysis of candidate Rex sites revealed remarkable variations in functional repertoires of candidate Rex-regulated genes in various microorganisms. Most of the reconstructed regulatory interactions are lineage specific, suggesting frequent events of gain and loss of regulator binding sites in the evolution of Rex regulons. We identified more than 50 novel Rex-regulated operons encoding functions that are essential for resumption of the NADH:NAD(+) balance. The novel functional role of Rex in the control of the central carbon metabolism and hydrogen production genes was validated by in vitro DNA binding assays using the TM0169 protein in the hydrogen-producing bacterium Thermotoga maritima.
Subject(s)
Carbon/metabolism , Energy Metabolism , Gene Expression Regulation, Bacterial , Gram-Positive Bacteria/genetics , Gram-Positive Bacteria/metabolism , NAD/metabolism , Repressor Proteins/metabolism , Binding Sites , DNA, Bacterial/metabolism , Operon , Oxidation-Reduction , Protein Binding , RegulonABSTRACT
Besides its function as an essential redox cofactor, nicotinamide adenine dinucleotide (NAD) also serves as a consumable substrate for several reactions with broad impact on many cellular processes. NAD homeostasis appears to be tightly controlled, but the mechanism of its regulation is little understood. Here we demonstrate that a previously predicted bacterial transcriptional regulator, NrtR, represses the transcription of NAD biosynthetic genes in vitro. The NAD metabolite ADP-ribose functions as an activator suppressing NrtR repressor activity. The presence of high ADP-ribose levels in the cell is indicative of active NAD turnover in bacteria, which could signal the activation of NAD biosynthetic gene expression via inhibiting the repressor function of NrtR. By comparing the crystal structures of NrtR in complex with DNA and with ADP-ribose, we identified a "Nudix switch" element that likely plays a critical role in the allosteric regulation of DNA binding and repressor function of NrtR.
