ABSTRACT
The proenzyme has very little adenosine diphosphate ribosyl transferase activity in vitro unless activated by simultaneous treatment with a denaturant, such as urea, and a reducing agent, such as dithiothreitol. Pseudomonas aeruginosa is a common, opportunistic, nosocomial pathogen infecting patients with weakened immunity, such as those with burns. Although a comprehensive functional map of the active site is still unavailable, several workers nevertheless have identified specific amino acids in domain III that are essential for the enzymic activity of the toxin. Since the discovery in 1966 that the lactose repressor protein is responsible for the selective induction of ß-galactosidase by E. coli in the presence of lactose, extensive studies have been made both on the lactose repressor, the bacteriophage lambda repressor, and other bacterial gene-regulating proteins. The transcriptional start site for the exotoxin A gene has been investigated by SI nuclease mapping.
