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The bvg‐dependent promoters show similar behaviour in different Bordetella species and share sequence homologies
No full textThe expression of the virulence‐associated genes in Bordetella species is co‐ordinately regulated by the gene products encoded by the bvg locus. In Bordetella pertussis the expression of this locus is regulated by the P1, P2, P3 and P4 promoters which are located in a 350bp DNA fragment also containing the PFHA promoter. Here we report the transcriptional regulation of the bvg locus and the fha gene in Bordetella paraper‐tussis and a sequence analysis of the byg‐regulated promoters. The Pp1, Pp2, Pp4 and PpFHA promoters are indistinguishable, both in transcription initiation sites and environmental regulation, from the corresponding promoters of B. pertussis, while the Pp3 promoter is not active. Sequence homologies from nine bvg‐regulated promoters show a conserved dinucleotide, 5′‐TG‐3′, at approximately one turn of helix upstream of the ‐10 5′‐A.AaTat‐3’region, and a 5′‐TTTCC‐3’sequence in the ‐90 region. Since the nucleotide sequence of the inactive Pp3 promoter shows several base substitutions with respect to the found sequence homologies, it is likely that some of these bases play an essential role in promoter activity. Copyright © 1991, Wiley Blackwell. All rights reserve
Sequential activation and environmental regulation of virulence genes in Bordetella pertussis
No full textBacterial pathogens undergo profound physiological changes when they infect their host and require coordinated regulation of gene expression in response to the stress encountered during infection. In Bordetella pertussis, the human pathogen which causes whooping cough, virulence factors are synthesized in response to environmental signals under the control of the bvg regulatory locus. Here we demonstrate that the bvg locus is responsible for two events of gene activation. In the first step the bvg locus transactivates its own autoregulated promoter (P1) and the promoter of the adherence factor filamentous haemagglutinin (P(FHA)). The second step occurs several hours later and consists of the transactivation of adenylate cyclase and pertussis toxin genes. We provide evidence that the second step of transactivation requires overexpression of regulatory proteins. Our results imply that bacterial adhesion and tissue colonization-intoxication are two separate steps at the molecular level
Positive transcriptional feedback at the bvg locus controls expression of virulence factors in Bordetella pertussis
No full textRegulation of the genes coding for virulence factors in Bordetella pertussis is controlled by the bvg locus, which encodes one putative sensory protein (BvgS) and one positive regulator of transcription (BvgA). We have studied the transcription of the bvg locus and found that this is controlled by a 350-base-pair DNA fragment, which contains five promoters, three of which transcribe the bvg locus, one transcribes an antisense RNA, and one transcribes a virulence-associated gene. Under noninducing conditions, only the promoter P2 is active and this is responsible for the production of low amounts of regulatory proteins. Upon induction, the other four promoters become active and, by a mechanism that may involve transcriptional and translational regulation, cause a 50-fold increase of the transcriptional activator BvgA. A model of the autoregulation of the bvg locus is presented
Erratum: Positive transcriptional feedback at the bvg locus controls expression of virulence factors in Bordetella pertussis (Proc. Natl. Acad. Sci. USA (September 1990) 87 (6753-6757))
No full textTHERMOREGULATION CONTROLS TWO STEPS OF VIRULENCE GENE-EXPRESSION IN BORDETELLA-PERTUSSIS
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Response of the bvg regulon of Bordetella pertussis to different temperatures and short-term temperature shifts
No full textBordetella pertussis produces a number of virulence factors whose expression is coordinately regulated by the bvgAS locus. Transcription of virulence genes is repressed by environmental factors such as low temperature (25°C) and chemical stimuli. Temperature shift of bacterial cultures from 25°C to 37°C activates two classes of bvg-regulated virulence genes: the early genes, which are activated within 10 min, and late genes, which require 2-4 h for activation. During the interval between the activation of the early and late genes, the intracellular concentration of BvgA increases 50-fold. It has been proposed that this increased concentration may be required for the activation of the late genes. Here we have analysed the response of the bvg locus to intermediate temperatures and to repeated temperature shifts. Temperature shifts of B. pertussis cultures from 22°C to 28°C, 32°C or 35°C resulted in the synthesis of low, intermediate, and high amounts of BvgA. This implied that the intracellular concentration of BvgA is temperature-dependent. We have also observed that the amount of virulence factors produced correlates with the BvgA concentration. When bacteria grown at 37°C were shifted to 22°C, transcription from the adenylate cyclase toxin haemolysis promoter (P(AC)) was repressed after 30 min, while transcription from the bvg (P1,) and filamentous haemagglutinin (P(FHA)) promoters was repressed after 2 h. During this time, the amount of BvgA did not decrease. A subsequent temperature shift from 22°C to 37°C induced transcription from the P1 and P(FHA) promoters after 10 min and transcription from the P(AC) promoter after 20 min. This result shows that in the presence of a high concentration of BvgA, the time lag between temperature shift and late promoter transcription is reduced from 2-4 h to 20 min. The above data support the proposal that the concentration of BvgA plays a role in activating expression of the late genes
Genetic characterization of Bordetella pertussis filamentous haemagglutinin: a protein processed from an unusually large precursor
No full textThe nucleotide sequence of the structural gene for filamentous haemagglutinin (FHA), fhaB, a crucial adherence factor for Bordetella perfussis, has been determined. Its 10774 nucleotides are far more than necessary to encode the 220kD biologically active, mature polypeptide product, suggesting a role for co‐or post‐translational processing. Fusion proteins derived from various portions of the fhaB open reading frame (ORF) were used to generate polyclonal antisera. Western immunoblot analysis of purified FHA and Bordetella sp. whole cell extracts with these antisera indicated that the 220kD product is encoded by the 5 portion of the ORF and that the smaller polypeptide species are breakdown products of this polypeptide. These data, as well as N‐terminal amino acid sequencing of the major polypeptide species, suggest a scheme for the proteolytic processing of an FHA precursor polypeptide. Copyright © 1990, Wiley Blackwell. All rights reserve
Magnesium(II)-induced effects on the stability of the Adenoside-Thymidine complex in solution
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