FIG. 1.

Expression and regulation of V. cholerae higBA. (A) Schematic representation of the higBA region of V. cholerae chromosome II, drawn approximately to scale. Thick arrows show genes, as annotated by TIGR, pointed in the direction of transcription. Bent arrows show the locations of the experimentally determined higBA promoter and the predicted higA promoter. The filled rectangle corresponds to the first 22 aa codons of annotated higB, which are not believed to be translated (see Fig. 2). Hatched areas denote regions deleted from higB and higA. Open rectangles show regions cloned to generate transcriptional reporter fusions in phigBlacZ and phigAlacZ. Thin arrows show regions transcribed in vitro to generate antisense riboprobes. (B) Northern blot of RNAs from wt, higB, and higBA strains of V. cholerae grown in either M63 or LB medium to various densities. The blot was probed with a riboprobe complementary to higA transcripts. (C) Northern blot as described for panel B, but probed with a riboprobe complementary to higB transcripts. (D) Northern blot of RNAs from wt V. cholerae grown in LB medium and treated with a variety of stresses. Cultures were grown at 37°C to an OD₆₀₀ of ∼0.7 (left and right panels) or 0.5 (middle panel) and then either left at 37°C for an additional 20 min (control [C]) or incubated with carbenicillin (50 μg/ml [Cb]) or chloramphenicol (1 to 10 μg/ml [Cm]) for 20 min, with kanamycin (50 to 500 μg/ml [Kn]) or spectinomycin (50 to 100 μg/ml [Sp]) for 1 h, or with spectinomycin (500 μg/ml) or mitomycin C (20 ng/ml [M]) for 20 min. Heat-treated cells were shifted either to 42°C for 20 min or to 50°C for 10 min. The blot was probed with a riboprobe complementary to higB transcripts. (E) β-Galactosidase activities (Miller units) from a higB::lacZ transcriptional reporter fusion (phigBlacZ) in wt, higB, and higBA strains of V. cholerae. Data are averages for at least three experiments. (F) β-Galactosidase activities (Miller units) from a higA::lacZ transcriptional reporter fusion (phigAlacZ) in wt, ΔhigB, and ΔhigBA strains of V. cholerae. Data are averages for at least three experiments.