DETECTION OF A PRFA-INDEPENDENT PROMOTER RESPONSIBLE FOR LISTERIOLYSIN GENE-EXPRESSION IN MUTANT LISTERIA-MONOCYTOGENES STRAINS LACKING THEPRFA REGULATOR

Expression of listeriolysin, a major virulence factor of pathogenic Li steria monocytogenes, is positively regulated by the pleiotropic virul ence regulator PrfA. In this study, we demonstrate that L. monocytogen es strains lacking the prfA regulator gene produce listeriolysin in sm all, albeit detectable, amounts when analyzed in a hemolysin assay and by immunoblots with listeriolysin-specific monoclonal antibodies. Tra nscriptional analysis revealed the existence of a PrfA-independent pro moter that was responsible for the hemolytic activity expressed by the se strains.