FIG. 3.

Reciprocal exchange of the classical and El Tor tcpPH promoter regions in V. cholerae. (A) Promoter deletion and replacement plasmids and strains. The divergently transcribed coding regions of tcpI and tcpP are indicated by the large black arrows at the top, and the intergenic region is shown by the solid line. The small arrow denotes the start of the tcpPH message. Striped black-white and gray-black boxes represent the regions of tcpI and tcpP from classical and El Tor, respectively, present in the plasmids (indicated at the left), and dotted lines represent intervening DNA which was deleted. Solid black and gray boxes represent classical and El Tor promoter regions, respectively. The strains generated by allelic exchange from the plasmids are indicated to the right. CL, classical; ET, El Tor; C/C, classical with classical promoter; C/E, classical with El Tor promoter; E/E, El Tor with El Tor promoter; E/C, El Tor with classical promoter. E, EcoRI; S, ScaI; N, NotI; K, KpnI. The asterisk shows the position of the seamless junction created using EarI. (B) Expression of tcpP-lacZ. Cultures were grown in LB medium (pH 6.5) at 30°C (left) and in AKI medium at 37°C (right). Black bars, strains with classical (CL) promoter regions: KSK618 (wild type [WT]); GK318 (C/C control); GK321 (E/C hybrid). Gray bars, strains with El Tor (ET) promoter regions: KSK725 (wild type); GK323 (E/E control); GK319 (C/E hybrid). Error bars show standard deviations.