The virR gene, a member of a class of two-component response regulators, regulates the production of perfringolysin O, collagenase, and hemagglutinin in Clostridium perfringens.

The perfringolysin O (theta-toxin) gene (pfoA) of Clostridium perfringens was cloned into an Escherichia coli-C. perfringens shuttle vector, and the pfoA gene was expressed in mutants of C. perfringens 13 which lacked the production of perfringolysin O. One group (SI117) could express the pfoA gene, and the other (SI112) could not. A mutation in the regulatory system for pfoA gene expression was suspected in SI112. A chromosomal DNA library constructed from strain 13 was transformed into strain SI112 to identify the regulatory gene(s) for the pfoA gene. Five strains of 10,000 transformants restored perfringolysin O production. All contained a 2.5-kb DNA fragment. This fragment activated the transcription of the pfoA gene and also restored the production of collagenase (kappa-toxin) and hemagglutinin in strain SI112. Deletion analysis showed that a 1.25-kb region was sufficient for the trans activity, and sequence analysis disclosed that open reading frame 2 (ORF2) was located in this region. A homology search for the deduced amino acid sequence revealed that ORF2 was homologous to a response regulator in a two-component signal transduction system. ORF2 was designated virR, and it is suggested that the virR gene plays an important role in the pathogenicity of C. perfringens.