FIG 3.

Overriding of PtvR-dependent transcriptional repression by the spxB promoter. (A) The transcripts of the ptv genes in the spxB promoter insertion strains. The transcripts of ptvR, ptvA, ptvB, and ptvC were quantified by qRT-PCR in strain D39s (wild type [WT]) and two clonal derivatives with an insertion of the spxB promoter sequence immediately upstream of the ptvR start codon (TH5204 and TH5205) as in Fig. 1. ***, P < 0.001. (B) The PtvB protein of the spxB promoter insertion strains was detected by immunoblotting as for Fig. 2F. (C) The PtvB protein of the spxB promoter insertion strain TH5204 in the presence of the empty vector (pIB) or ptvR complementation construct (pIB::ptvR). Proteins were detected as for panel B. Episomal ptvR was unable to repress the expression of PtvB when the ptv promoter was separated from the downstream coding region by the spxB promoter (lane 3).