FIG. 2.

V. cholerae tolQRAB mutants (DH1, DH2, DH3, and DH4) produce amounts of TcpA similar to those produced by O395. All strains are derivatives of O395. The DH1 revertant was made by growing a small colony of DH1 in LB broth overnight at 37°C in the absence of ampicillin. The excision of pDH235 from tolQ in this revertant strain was confirmed by Southern analysis. All strains were grown in LB broth at 30°C. Whole-cell lysates were prepared in sample buffer as previously described (23) and run on an 4 to 12% Tris-Bis gradient gel (Novex, San Diego, Calif.). The proteins were then transferred to nitrocellulose and probed with anti-TcpA polyclonal antiserum.