FIG. 1.

Mapping of the AlgU-dependent oprF promoter. (A) Primer extension mapping of the mRNA 5′ end corresponding to the AlgU promoter of oprF. Total RNA was isolated from the algU⁺ mucA22 mucoid strain PAO578II and from its nonmucoid algU knockout derivative (algU::Tc^r; PAO6865) grown under conditions promoting the mucoid phenotype (Materials and Methods). Primer extension products were run adjacent to the sequencing ladder generated with the same primer used for reverse transcription. Vertical bars indicate the −35/−10 regions of the AlgU-dependent promoter of oprF. The nucleotide corresponding to the mRNA 5" end is designated P_AlgU with an asterisk. (B) Control for panel A, showing the presence of the oprF AlgU-independent promoter at −57 upstream of the initiation codon. In this particular gel, the intensity of the band in the algU lane was 17% stronger than in the algU::Tc^r mutant. (C) Primer extension of the previously mapped AlgU-dependent promoter P_D of algD, included here as a control (13). All procedures and designations as in panel A. (D) Maps showing the relative positions of the AlgU-dependent promoters upstream of the algD and oprF genes. A previously mapped oprF promoter, corresponding to the mRNA start site at −40, is dependent on the alternative sigma factor SigX (11). The promoter at −57 is regulated by an unknown sigma factor (17). All numbering is relative to the initiation codon.