Regulation of tricarboxylate transport and metabolism in ADP1.

Despite the significant presence of plant-derived tricarboxylic acids in some environments, few studies detail the bacterial metabolism of -aconitic acid (Taa) and tricarballylic acid (Tcb). In a soil bacterium, ADP1, we discovered interrelated pathways for the consumption of Taa and Tcb. An intricate regulatory scheme tightly controls the transport and catabolism of both compounds and may reflect that they can be toxic inhibitors of the tricarboxylic acid cycle.

Strain-Specific Gifsy-1 Prophage Genes Are Determinants for Expression of the RNA Repair Operon during the SOS Response in Salmonella enterica Serovar Typhimurium.

The adaptation of Salmonella enterica serovar Typhimurium to stress conditions involves expression of genes within the regulon of the alternative sigma factor RpoN (σ). RpoN-dependent transcription requires an activated bacterial enhancer binding protein (bEBP) that hydrolyzes ATP to remodel the RpoN-holoenzyme-promoter complex for transcription initiation. The bEBP RtcR in Typhimurium strain 14028s is activated by genotoxic stress to direct RpoN-dependent expression of the RNA repair operon The molecular signal for RtcR activation is an oligoribonucleotide with a 3'-terminal 2',3'-cyclic phosphate.

Binding of 2',3'-Cyclic Nucleotide Monophosphates to Bacterial Ribosomes Inhibits Translation.

The intracellular small molecules 2',3'-cyclic nucleotide monophosphates (2',3'-cNMPs) have recently been rediscovered within both prokaryotes and eukaryotes. Studies in bacteria have demonstrated that 2',3'-cNMP levels affect bacterial phenotypes, such as biofilm formation, motility, and growth, and modulate expression of numerous genes, suggesting that 2',3'-cNMP levels are monitored by cells. In this study, 2',3'-cNMP-linked affinity chromatography resins were used to identify proteins that bind 2',3'-cNMPs, with the top hits including all of the ribosomal proteins, and to confirm direct binding of purified ribosomes.

Regulation of l- and d-Aspartate Transport and Metabolism in Acinetobacter baylyi ADP1.

The regulated uptake and consumption of d-amino acids by bacteria remain largely unexplored, despite the physiological importance of these compounds. Unlike other characterized bacteria, such as Escherichia coli, which utilizes only l-Asp, Acinetobacter baylyi ADP1 can consume both d-Asp and l-Asp as the sole carbon or nitrogen source. As described here, two LysR-type transcriptional regulators (LTTRs), DarR and AalR, control d- and l-Asp metabolism in strain ADP1.

Cellular Effects of 2',3'-Cyclic Nucleotide Monophosphates in Gram-Negative Bacteria.

Organismal adaptations to environmental stimuli are governed by intracellular signaling molecules such as nucleotide second messengers. Recent studies have identified functional roles for the noncanonical 2',3'-cyclic nucleotide monophosphates (2',3'-cNMPs) in both eukaryotes and prokaryotes. In Escherichia coli, 2',3'-cNMPs are produced by RNase I-catalyzed RNA degradation, and these cyclic nucleotides modulate biofilm formation through unknown mechanisms.

In silico simulations of occurrence of transcription factor binding sites in bacterial genomes.

Background: Interactions between transcription factors and their specific binding sites are a key component of regulation of gene expression. Until recently, it was generally assumed that most bacterial transcription factor binding sites are located at or near promoters. However, several recent works utilizing high-throughput technology to detect transcription factor binding sites in bacterial genomes found a large number of binding sites in unexpected locations, particularly inside genes, as opposed to known or expected promoter regions.

Genotoxic, Metabolic, and Oxidative Stresses Regulate the RNA Repair Operon of Salmonella enterica Serovar Typhimurium.

The σ regulon in serovar Typhimurium includes a predicted RNA repair operon encoding homologs of the metazoan Ro60 protein (Rsr), Y RNAs (YrlBA), RNA ligase (RtcB), and RNA 3'-phosphate cyclase (RtcA). Transcription from σ-dependent promoters requires that a cognate bacterial enhancer binding protein (bEBP) be activated by a specific environmental or cellular signal; the cognate bEBP for the σ-dependent promoter of the operon is RtcR. To identify conditions that generate the signal for RtcR activation in Typhimurium, transcription of the RNA repair operon was assayed under multiple stress conditions that result in nucleic acid damage.

Malonate degradation in ADP1: operon organization and regulation by MdcR.

Transcriptional regulators in the LysR or GntR families are typically encoded in the genomic neighbourhood of bacterial genes for malonate degradation. While these arrangements have been evaluated using bioinformatics methods, experimental studies demonstrating co-transcription of predicted operons were lacking. Here, transcriptional regulation was characterized for a cluster of genes that enable a soil bacterium, ADP1, to use malonate as a carbon source.

Novel DNA Binding and Regulatory Activities for σ (RpoN) in Salmonella enterica Serovar Typhimurium 14028s.

The variable sigma (σ) subunit of the bacterial RNA polymerase (RNAP) holoenzyme, which is responsible for promoter specificity and open complex formation, plays a strategic role in the response to environmental changes. serovar Typhimurium utilizes the housekeeping σ and five alternative sigma factors, including σ The σ-RNAP differs from other σ-RNAP holoenzymes in that it forms a stable closed complex with the promoter and requires ATP hydrolysis by an activated cognate bacterial enhancer binding protein (bEBP) to transition to an open complex and initiate transcription. In Typhimurium, σ-dependent promoters normally respond to one of 13 different bEBPs, each of which is activated under a specific growth condition.

Modulating Salmonella Typhimurium's Response to a Changing Environment through Bacterial Enhancer-Binding Proteins and the RpoN Regulon.

Transcription sigma factors direct the selective binding of RNA polymerase holoenzyme (Eσ) to specific promoters. Two families of sigma factors determine promoter specificity, the σ(70) (RpoD) family and the σ(54) (RpoN) family. In transcription controlled by σ(54), the Eσ(54)-promoter closed complex requires ATP hydrolysis by an associated bacterial enhancer-binding protein (bEBP) for the transition to open complex and transcription initiation.

Use of a promiscuous, constitutively-active bacterial enhancer-binding protein to define the σ⁵⁴ (RpoN) regulon of Salmonella Typhimurium LT2.

Background: Sigma54, or RpoN, is an alternative σ factor found widely in eubacteria. A significant complication in analysis of the global σ⁵⁴ regulon in a bacterium is that the σ⁵⁴ RNA polymerase holoenzyme requires interaction with an active bacterial enhancer-binding protein (bEBP) to initiate transcription at a σ⁵⁴-dependent promoter. Many bacteria possess multiple bEBPs, which are activated by diverse environmental stimuli.

Analysis of IS1236-mediated gene amplification events in Acinetobacter baylyi ADP1.

Recombination between insertion sequence copies can cause genetic deletion, inversion, or duplication. However, it is difficult to assess the fraction of all genomic rearrangements that involve insertion sequences. In previous gene duplication and amplification studies of Acinetobacter baylyi ADP1, an insertion sequence was evident in approximately 2% of the characterized duplication sites.

Site-specific insertion of IS492 in Pseudoalteromonas atlantica.

Reversible insertion of IS492 at a site within epsG on the Pseudoalteromonas atlantica chromosome controls peripheral extracellular polysaccharide production and biofilm formation by P. atlantica. High-frequency precise excision of IS492 from epsG requires 5 and 7 bp of flanking DNA, suggesting that IS492 transposition involves a site-specific recombination mechanism.

Chromosomal context directs high-frequency precise excision of IS492 in Pseudoalteromonas atlantica.

DNA rearrangements, including insertions, deletions, and inversions, control gene expression in numerous prokaryotic and eukaryotic systems, ranging from phase variation of surface antigens in pathogenic bacteria to generation of Ig diversity in human B cells. We report here that precise excision of the mobile element IS492 from one site on the Pseudoalteromonas atlantica chromosome directly correlates with phase variation of peripheral extracellular polysaccharide ((p)EPS) production from OFF (epsG::IS492) to ON (epsG(+)). In a previously undescribed application of quantitative PCR, we determined that the frequency of this transposase-dependent precise excision is remarkably high, ranging from 10(-3) to 10(-2) per cell per generation.

Piv site-specific invertase requires a DEDD motif analogous to the catalytic center of the RuvC Holliday junction resolvases.

Piv, a unique prokaryotic site-specific DNA invertase, is related to transposases of the insertion elements from the IS110/IS492 family and shows no similarity to the site-specific recombinases of the tyrosine- or serine-recombinase families. Piv tertiary structure is predicted to include the RNase H-like fold that typically encompasses the catalytic site of the recombinases or nucleases of the retroviral integrase superfamily, including transposases and RuvC-like Holliday junction resolvases. Analogous to the DDE and DEDD catalytic motifs of transposases and RuvC, respectively, four Piv acidic residues D9, E59, D101, and D104 appear to be positioned appropriately within the RNase H fold to coordinate two divalent metal cations.

Analysis of the Piv recombinase-related gene family of Neisseria gonorrhoeae.

Neisseria gonorrhoeae (the gonococcus) is an obligate human pathogen and the causative agent of the disease gonorrhea. The gonococcal pilus undergoes antigenic variation through high-frequency recombination events between unexpressed pilS silent copies and the pilin expression locus pilE. The machinery involved in pilin antigenic variation identified to date is composed primarily of genes involved in homologous recombination.