Regulation of Expression of Type I Signal Peptidases in Listeria Monocytogenes

The role of type I signal peptidases (SPases I) is to remove the signal peptides of preproteins exported by the general secretory pathway. The genome ofListeria monocytogenescontains a locus encoding three contiguous SPases I (denoted SipX, SipY and SipZ). The authors recently showed that SipX and SipZ perform distinct functions in protein secretion and bacterial pathogenicity. Here, the regulation ofsipgene expression in broth and in infected eukaryotic cells was studied. The results show that expression of the threesipgenes is (i) controlled by two distinct promoter regions that respond differently to growth phase and temperature variations, and (ii) influenced by PrfA (the transcriptional activator regulating most of the virulence genes ofL. monocytogenes) and the stress proteins ClpC and ClpP. It was found thatsipgene expression was strongly upregulated upon infection of eukaryotic cells when bacteria were still entrapped in the phagosomal compartment. This upregulation is compatible with the need ofL. monocytogenesto optimize its production of virulence factors in the early stage of the intracellular cycle.