CtsR controls class III heat shock gene expression in the human pathogen Listeria monocytogenes

Stress proteins play an important role in virulence, yet little is known ab out the regulation of stress response in pathogens. In the facultative intr acellular pathogen Listeria monocytogenes, the Clp ATPases, including ClpC, ClpP and ClpE, are required for stress survival and intracellular growth. The first gene of the clpC operon of L. monocytogenes encodes a homologue o f the Bacillus subtilis CtsR repressor of stress response genes. An L. mono cytogenes ctsR-deleted mutant displayed enhanced survival under stress cond itions (growth in the presence of 2% NaCl or at 42 degrees C), but its leve l of virulence in the mouse was not affected. The virulence of a wild-type strain constitutively expressing CtsR is significantly attenuated, presumab ly because of repression of the stress response. Regulation of the L. monoc ytogenes clpC, clpP and clpE genes was investigated using transcriptional f usions in B. subtilis as a host. The L. monocytogenes ctsR gene was placed under the control of an inducible promoter, and regulation by CtsR and heat shock was demonstrated in vivo in B. subtilis. The purified CtsR protein o f L. monocytogenes binds specifically to the clpC, clpP and clpE regulatory regions, and the extent of the CtsR binding sites was defined by DNase I f ootprinting. Our results demonstrate that this human pathogen possesses a C tsR regulon controlling class III heat shock genes, strikingly similar to t hat of the saprophyte B. subtilis. This is the first description of a stres s response regulatory gene in a pathogen.