Transcriptional activation of the Listeria monocytogenes hemolysin gene in Bacillus subtilis

The prfA gene of Listeria monocytogenes was recently reported to be required for expression of hly, which encodes a pore-forming hemolysin essential for pathogenicity (M. Leimeister-Wachter, C. Haffner, E. Domann, W. Goebel, and T. Chakraborty, Proc. Natl. Acad. Sci. USA 87:8336-8340, 1990). We demonstrate here that a hly-lacZ fusion introduced into Bacillus subtilis is strongly activated when the prfA gene product is supplied in trans under the control of an isopropyl-beta-D-thiogalactopyranoside-inducible promoter, Pspac. Moreover, the PrfA-dependent activation of hly is abolished by point mutations in a 14-bp DNA palindromic sequence present in the 5' upstream region of hly. This indicates that PrfA is both necessary and sufficient for hly transcriptional activation and establishes the palindrome as the likely target sequence for PrfA interaction. The presence of a palindrome in the upstream regions of three additional L. monocytogenes genes clustered near hly suggests that PrfA may serve as a transcriptional activator for a major virulence regulon of L. monocytogenes. In addition, the ability of PrfA to activate its target promoters effectively in B. subtilis suggests that further analysis of this regulon and perhaps other aspects of L. monocytogenes gene regulation might be carried out in part through reconstruction experiments in B. subtilis.