The Salmonella enterica Serovar Typhi LeuO Global Regulator Forms Tetramers: Residues Involved in Oligomerization, DNA Binding, and Transcriptional Regulation (original) (raw)
Related papers
2008
LeuO is a LysR-type transcriptional regulator that has been implicated in the bacterial stringent response and in the virulence of Salmonella. A genomic analysis with Salmonella enterica serovar Typhi revealed that LeuO is a positive regulator of OmpS1, OmpS2, AssT, and STY3070. In contrast, LeuO down-regulated the expression of OmpX, Tpx, and STY1978. Transcriptional fusions supported the positive and negative LeuO regulation. Expression of ompS1, assT, and STY3070 was induced in an hns mutant, consistent with the notion that H-NS represses these genes; transcriptional activity was lower for tpx and STY1978 in an hns background, suggesting that this global regulatory protein has a positive effect. In contrast, ompS2 and ompX expression appeared to be H-NS independent. LeuO specifically bound to the 5 intergenic regions of ompS2, assT, STY3070, ompX, and tpx, while it was not observed to bind to the promoter region of STY1978, suggesting that LeuO regulates in direct and indirect ways. In this work, a novel set of genes belonging to the LeuO regulon are described; interestingly, these genes are involved in a variety of biological processes, suggesting that LeuO is a global regulator in Salmonella. Salmonella enterica serovar Typhi is a gram-negative facultative intracellular pathogen that causes typhoid fever in humans. The complete genomic sequence of Salmonella serovar Typhi is composed of a 4.8-Mb chromosome and two small replicons (218 and 106 kb). The genome includes 250 genes involved in transcriptional regulatory functions (41). LeuO belongs to the LysR family of transcription regulators present in Enterobacteriaceae such as Yersinia, Shigella, Escherichia coli, and Salmonella; these regulators typically are 300 amino acids long and have an N-terminal DNA binding domain and a C-terminal sensing domain. They can function as activators or repressors and regulate genes with promoters that are divergent from their own promoter. The family of LysR transcriptional factors is involved in microbe-plant and microbe-animal interactions (48). The LeuO regulator has been reported to be a virulence factor in Caenorhabditis elegans and in the mouse model with Salmonella (26, 46, 52). LeuO expression is enhanced in stationary phase and by phosphorous restriction (10, 56); it is also involved in Vibrio cholerae biofilm formation and in the stringent response (30, 35). LeuO regulates the bgl and cadAB operons, as well as the ompS1, ompS2, dsrA, and rovA genes (5, 12, 27, 45, 50, 55), and has been shown to be part of a promoter relay mechanism that explains the coordinate expression of the ilvIH-leuO-leuABCD gene cluster (9). In this
Nucleic Acids Research, 2012
Ler is a DNA-binding, oligomerizable protein that regulates pathogenicity islands in enterohemorrhagic and enteropathogenic Escherichia coli strains. Ler counteracts the transcriptional silencing effect of H-NS, another oligomerizable nucleoidassociated protein. We studied the oligomerization of Ler in the absence and presence of DNA by atomic force microscopy. Ler forms compact particles with a multimodal size distribution corresponding to multiples of 3-5 units of Ler. DNA wraps around Ler particles that contain more than 15-16 Ler monomers. The resulting shortening of the DNA contour length is in agreement with previous measurements of the length of DNA protected by Ler in footprinting assays. We propose that the repetition unit corresponds to the number of monomers per turn of a tight helical Ler oligomer. While the repressor (H-NS) and anti-repressor (Ler) have similar DNA-binding domains, their oligomerization domains are unrelated. We suggest that the different oligomerization behavior of the two proteins explains the opposite results of their interaction with the same or proximal regions of DNA.
leu operon of Salmonella typhimurium is controlled by an attenuation mechanism
Proceedings of the National Academy of Sciences, 1979
The nucleotide sequence of the control region of the leu operon of Salmonella typhimurium was determined. A prominent feature of this region is a signal for termination of transcription. In vitro, transcription does terminate at this site, yielding a leader RNA of about 160 nucleotides as a major product. This leader RNA is potentially translatable into a peptide containing 28 amino acids, 4 of which are adjacent leucine residues. Several regions of base complementarity exist within the leader, positioned such that pairing of one region precludes pairing of another. The position of the four leucine codons relative to two regions of base complementarity suggest a model for the regulation of the leu operon similar to that proposed by Yanofsky and coworkers for the trp operon. In addition, a third region of base complementarity was identified which, when incorporated into the model, explains why premature termination is the usual outcome when transcription is initiated in vitro by puri...
STRUCTURAL STUDIES OF TRANSCRIPTIONAL REGULATION BY LysR-TYPE TRANSCRIPTIONAL REGULATORS IN BACTERIA
Reviews in Agricultural Science, 2018
LysR-type transcriptional regulators (LTTRs) comprise one of the largest families of transcriptional regulators in bacteria and control gene expression of various types of metabolic, virulence and physiological functions. LTTRs typically form homotetramers and require an inducer molecule(s) to activate the transcription of target genes. The N-terminal region of LTTRs contains a DNAbinding domain (DBD) with the winged helix-turn-helix motif that specifically binds the promoter region of target genes. The C-terminal region of LTTRs is connected to the DBD by a linker helix and forms the regulatory domain (RD) that contains a binding pocket for inducer molecules. Crystal structures of several LTTR family members together with their biochemical analyses have provided a potential mechanism for the initial process of transcriptional activation by LTTRs. First, helix 3 of the winged helix-turn-helix motif in DBD is supposed to distinguish the recognition binding site (RBS) in the promoter region, resulting in complex formation through interactions between two DBDs in the tetrameric LTTR and RBS. Formation of this complex seems to enable interactions between the other two DBDs in the LTTR tetramer and the activation binding site (ABS) in the promoter region. The binding of the tetrameric LTTR to both the RBS and ABS causes the promoter DNA to adopt a bent structure because the four DBDs in the tetrameric LTTR are arranged in a V-shaped manner at the bottom of the LTTR. Interaction of an inducer molecule(s) with the RD seems to cause a quaternary structural change of the LTTR that relaxes the bending angle of the promoter DNA with a concomitant shift of the bound DBDs at the ABS. These events facilitate recruitment of RNA polymerase to its binding site in the promoter region, which overlaps with the ABS for LTTR.
Transcription initiation sites of the leucine operons of Salmonella typhimurium and Escherichia coli
Journal of Molecular Biology, 1983
Evidence for a transcription attenuation site downstream from the leu promoter was obtained by transcription experiments in vitro. Most transcription initiated in vitro from teuP is terminated prematurely, resulting in the synthesis of a 160 nucleotide leader RNA. We define here the point at which transcription is initiated in vitro and in vivo and demonstrate that the site of premature termination is between the promoter and the first structural gene (leuA). Additional nucleotide sequences are presented that extend the known sequence 200 base-pairs upstream and 300 base-pairs downstream from leuP. The location of the promoter-proximal end of cistron leuA was deduced by comparing nucleotide sequence data with the sequence of the ten amino acids at the N-terminus of a-isopropylmalate synthase. To facilitate the isolation of quantities of material for sequencing experiments, the enzyme was isolated from a plasmid-containing strain, CV605, grown under conditions of leucine limitation. Under such conditions, about 20% of the total soluble protein of strain CV605 is a-isopropylmalate synthase and another 20~/o is fl-isopropylmalate dehydrogenase (leuB product).
Frontiers in immunology, 2014
Salmonella are facultative intracellular pathogens. Salmonella infection occurs mainly by expression of two Salmonella pathogenicity Islands (SPI-1 and SPI-2). SPI-1 encodes transcriptional factors that participate in the expression of virulence factors encoded in the island. However, there are transcriptional factors encoded outside the island that also participate in the expression of SPI-1-encoded genes. Upon infection, bacteria are capable of avoiding the host immune response with several strategies that involve several virulence factors under the control of transcriptional regulators. Interestingly, LeuO a transcriptional global regulator which is encoded outside of any SPI, is proposed to be part of a complex regulatory network that involves expression of several genes that help bacteria to survive stress conditions and, also, induces the expression of porins that have been shown to be immunogens and can thus be considered as antigenic candidates for acellular vaccines. Hence,...