The Listeria monocytogenes prfAP2 promoter is regulated by sigma B in a growth phase dependent manner

Listeria monocytogenes prfA, encoding positive regulatory factor A, is transcribed from three promoters (prfAP1, prfAP2, and PplcA). The prfAP2 promoter was previously proposed to be sigma B (σB)-dependent. This hypothesis was tested by creating prfA promoter-gus transcriptional fusions in both L. monocytogenes wild-type (wt) and ΔsigB backgrounds and then measuring (i) β-glucuronidase (GUS) activities; (ii) gus mRNA transcript levels; and (iii) the presence or absence of GUS in cells by immunofluorescence staining. prfAP2-directed expression increased as the wt L. monocytogenes strain entered stationary phase, whereas prfAP2-directed expression was greatly reduced in the ΔsigB strain, confirming both growth phase- and σB-dependent transcription of prfAP2. We conclude that prfAP2 is directly regulated by σB.