Transcription Activation Parameters at

Zhang, Xin; Reeder, Thadd; Schleif, Robert

doi:10.1006/jmbi.1996.0230

Cited by 62 publications

(80 citation statements)

References 53 publications

(59 reference statements)

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“…HilD contains a C-terminal helix-turn-helix DNA-binding motif within a conserved 99-amino-acid domain characteristic of AraC/XylS family members (42). These transcriptional regulators are generally considered to activate transcription by direct contact and recruitment of RNA polymerase to their cognate promoters (7,26,37,51). A current model for HilD function postulates a novel role for an AraC/XylS regulator by suggesting that HilD acts as a derepressor to counteract the effects of negative regulators that bind upstream of Ϫ39 on the hilA promoter.…”

Section: Discussionmentioning

confidence: 99%

Transcription of theSalmonellaInvasion Gene Activator,hilA, Requires HilD Activation in the Absence of Negative Regulators

2003

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Salmonella enterica serovar Typhimurium causes human gastroenteritis and a systemic typhoid-like infection in mice. Infection is initiated by entry of the bacteria into intestinal epithelial cells and is mediated by a type III secretion system that is encoded by genes in Salmonella pathogenicity island 1. The expression of invasion genes is tightly regulated by environmental conditions such as oxygen and osmolarity, as well as by many bacterial factors. The hilA gene encodes an OmpR/ToxR family transcriptional regulator that activates the expression of invasion genes in response to both environmental and genetic regulatory factors. HilD is an AraC/XylS regulator that has been postulated to act as a derepressor of hilA expression that promotes transcription by interfering with repressor binding at the hilA promoter. Our research group has identified four genes (hilE, hha, pag, and ams) that negatively affect hilA transcription. Since the postulated function of HilD at the hilA promoter is to counteract the effects of repressors, we examined this model by measuring hilA::Tn5lacZY expression in strains containing negative regulator mutations in the presence or absence of functional HilD. Single negative regulator mutations caused significant derepression of hilA expression, and two or more negative regulator mutations led to very high level expression of hilA. However, in all strains tested, the absence of hilD resulted in low-level expression of hilA, suggesting that HilD is required for activation of hilA expression, whether or not negative regulators are present. We also observed that deletion of the HilD binding sites in the chromosomal hilA promoter severely decreased hilA expression. In addition, we found that a single point mutation at leucine 289 in the C-terminal domain of the ␣ subunit of RNA polymerase leads to very low levels of hilA::Tn5lacZY expression, suggesting that HilD activates transcription of hilA by contacting and recruiting RNA polymerase to the hilA promoter.

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Section: Discussionmentioning

confidence: 99%

Transcription of theSalmonellaInvasion Gene Activator,hilA, Requires HilD Activation in the Absence of Negative Regulators

2003

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“…This construction placed the yoeB Spn gene under control of the arabinose-inducible P BAD promoter. Thus, when cells were grown in arabinose-containing medium, AraC was active and promoted transcription from the P BAD promoter, whereas when cells were grown in the presence of glucose, AraC was inactive and transcription from P BAD was switched off (54).…”

Section: Bacterialmentioning

confidence: 99%

TheyefM-yoeBToxin-Antitoxin Systems ofEscherichia coliandStreptococcus pneumoniae: Functional and Structural Correlation

et al. 2007

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Toxin-antitoxin loci belonging to the yefM-yoeB family are located in the chromosome or in some plasmids of several bacteria. We cloned the yefM-yoeB locus of Streptococcus pneumoniae, and these genes encode bona fide antitoxin (YefM Spn ) and toxin (YoeB Spn ) products. We showed that overproduction of YoeB Spn is toxic to Escherichia coli cells, leading to severe inhibition of cell growth and to a reduction in cell viability; this toxicity was more pronounced in an E. coli B strain than in two E. coli K-12 strains. The YoeB Spn -mediated toxicity could be reversed by the cognate antitoxin, YefM Spn , but not by overproduction of the E. coli YefM antitoxin. The pneumococcal proteins were purified and were shown to interact with each other both in vitro and in vivo. Far-UV circular dichroism analyses indicated that the pneumococcal antitoxin was partially, but not totally, unfolded and was different than its E. coli counterpart. Molecular modeling showed that the toxins belonging to the family were homologous, whereas the antitoxins appeared to be specifically designed for each bacterial locus; thus, the toxin-antitoxin interactions were adapted to the different bacterial environmental conditions. Both structural features, folding and the molecular modeled structure, could explain the lack of crosscomplementation between the pneumococcal and E. coli antitoxins.The gram-positive, spherical bacterium Streptococcus pneumoniae (pneumococcus) is the cause of many human diseases, such as pneumonia, bacterial blood poisoning (bacteremia), inflammation of the membranes surrounding the brain and spinal cord (meningitis), middle-ear infection (otitis media), osteomyelitis, septic arthritis, endocarditis, peritonitis, pericarditis, and sinusitis; pneumonia is the most severe disease (15,28). Although the pneumococcus can normally be found in the noses and throats of healthy individuals, it can grow and cause infection when the immune system is weakened. The people who are most at risk of developing pneumococcal pneumonia have a weakened immune system. These people include the elderly, infants, cancer patients, AIDS patients, postoperative patients, alcoholics, and people with diabetes. The global rate of mortality is more than 1,000,000 people per year, and this figure represents about 15 to 20% of the people infected.

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“…This relieves the constraints on the DNA-binding domains and allows them to bind to the adjacent direct repeat I 1 and I 2 half-sites. This mode of DNA binding allows AraC to activate RNA polymerase for transcription from p BAD (5)(6)(7)(8)(9).…”

mentioning

confidence: 99%

Strengthened Arm-Dimerization Domain Interactions in AraC

Schleif

2001

Journal of Biological Chemistry

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Constitutive mutations were sought and found in the N-terminal arm of the Escherichia coli regulatory protein of the arabinose operon, AraC protein. A new mutation, N16D, was of particular interest. Asn-16 is not seen in the crystal structure of the AraC dimerization domain determined in the absence of arabinose, because the N-terminal arm 18 residues are disordered, but in the presence of arabinose, residues 7-18 fold over the arabinose and make many interactions with it. In this state Asn-16 lies near two positively charged amino acids, Lys-43 and Arg-99. We propose that the introduction of the negatively charged aspartic residue at position 16 creates a charge-charge interaction network among Asp-16, Lys-43, and Arg-99 that holds the arm to the dimerization domain even in the absence of arabinose. This frees the DNA-binding domains and allows them to bind cis to I 1 -I 2 half-sites and activate transcription. Mutating the two positively charged residues to alanines individually and collectively decreased or eliminated the constitutivity created by the N16D mutation.

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Transcription Activation Parameters at

Cited by 62 publications

References 53 publications

Transcription of theSalmonellaInvasion Gene Activator,hilA, Requires HilD Activation in the Absence of Negative Regulators

Transcription of theSalmonellaInvasion Gene Activator,hilA, Requires HilD Activation in the Absence of Negative Regulators

TheyefM-yoeBToxin-Antitoxin Systems ofEscherichia coliandStreptococcus pneumoniae: Functional and Structural Correlation

Strengthened Arm-Dimerization Domain Interactions in AraC

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