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Cline, SD, Saleem, S and Daines, DA (2012) Regulation of the vapBC-1 toxin-antitoxin locus in nontypeable Haemophilus influenzae. PLoS ONE 7:e32199


Nontypeable Haemophilus influenzae (NTHi) are human-adapted commensal bacteria that can cause a number of chronic mucosal infections, including otitis media and bronchitis. One way for these organisms to survive antibiotic therapy and cause recurrent disease is to stop replicating, as most antimicrobials target essential biosynthetic pathways. Toxin-antitoxin (TA) gene pairs have been shown to facilitate entry into a reversible bacteriostatic state. Characteristically, these operons encode a protein toxin and an antitoxin that associate following translation to form a nontoxic complex, which then binds to and regulates the cognate TA promoter. Under stressful conditions, the labile antitoxin is degraded and the complex disintegrates, freeing the stable toxin to facilitate growth arrest. How these events affected the regulation of the TA locus, as well as how the transcription of the operon was subsequently returned to its normal state upon resumption of growth, was not fully understood. Here we show that expression of the NTHi vapBC-1 TA locus is repressed by a complex of VapB-1 and VapC-1 under conditions favorable for growth, and activated by the global transactivator Factor for Inversion Stimulation (Fis) upon nutrient upshift from stationary phase. Further, we demonstrate for the first time that the VapC-1 toxin alone can bind to its cognate TA locus control region and that the presence of VapB-1 directs the binding of the VapBC-1 complex in the transcriptional regulation of vapBC-1.


PubMed PMC3302801 Online version:10.1371/journal.pone.0032199


Antitoxins/genetics; Antitoxins/metabolism; Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Bacterial Toxins/genetics; Bacterial Toxins/metabolism; Cloning, Molecular; DNA Primers/genetics; DNA-Binding Proteins/genetics; DNA-Binding Proteins/metabolism; Electrophoretic Mobility Shift Assay; Gene Expression Regulation, Bacterial/genetics; Gene Expression Regulation, Bacterial/physiology; Haemophilus influenzae/genetics; Haemophilus influenzae/metabolism; Membrane Glycoproteins/genetics; Membrane Glycoproteins/metabolism; Multiprotein Complexes/genetics; Multiprotein Complexes/metabolism; Mutagenesis, Site-Directed; Promoter Regions, Genetic/genetics; Real-Time Polymerase Chain Reaction



Gene product Qualifier GO Term Evidence Code with/from Aspect Extension Notes Status


GO:0006355: regulation of transcription, DNA-dependent

IMP: Inferred from Mutant Phenotype:


Figure 2: fis is necessary for nutrient upshift activation of the vapBC-1 promoter driving lacZ.

CACAO 6005

See also


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