Transcriptional elements in Pasteurella haemolytica leukotoxin expression

Pasteurella haemolytica is the primary bacterial agent in bovine shipping fever pneumonia and produces and secretes a species-specific leukotoxin. The toxin is a member of the RTX family of cytolysins, and is maximally expressed during log-phase growth at 37 °C. We are examining the regulatory mechanisms involved in leukotoxin expression using operon fusions and trans-complementation in Escherichia coli. The leukotoxin promoter region contains a static DNA bend that enhances transcription. A trans-activator of this promoter has been isolated and partially characterized. A second, divergent promoter maps immediately upstream of the DNA bend and transcribes a gene encoding a periplasmic binding protein. This permease protein, and its associated nucleotide-binding and membrane spanning components, may be involved in sensory regulation of the leukotoxin in Pasteurella.