FnrP interactions with the Pasteurella haemolytica leukotoxin promoter

Pasteurella haemolytica FnrP is homologous to Fnr, the global transcription al regulator of anaerobic respiration in Escherichia roll. To investigate t he role of O-2 in the expression of P. haemolytica leukotoxin, we tested a lktC::lacZ fusion constructed in E. coli for a FnrP- mediated regulatory ef fect under aerobic and anaerobic growth conditions. Both E. coli Fnr and Fn rP suppressed leukotoxin transcription under aerobic conditions. Under anae robic conditions, Fnr suppressed transcription, while FnrP increased transc ription. These results were confirmed using FnrP*, a mutant form of FnrP th at activates anaerobically inducible genes under aerobic conditions. In mob ility shift assays, partially purified FnrP bound to a potential regulatory site in a P. haemolytica iktC promoter fragment. (C) 2000 Published by Els evier Science B.V. All rights reserved.