FIG. 2.

Na⁺ induction of plasmidic nhaA′-′lacZ fusion. (A) ΔnhaA ΔnhaR cells (OR200) transformed with the indicated plasmids were used. All plasmids carried an nhaA′-′lacZ fusion but differ in either the level of the encoded NhaR (−, none; +, moderate expression; ++, strong expression) and/or the nhaA promoters as indicated. Cells were grown exponentially for 1 h in LBK-BTP broth at pH 7.5 in the presence or absence of 100 mM NaCl. Expression was monitored as β-galactosidase activity in Miller units as described previously (16). (B) The plasmids and experimental procedure were as for panel A, but the host was OR200D1, a ΔnhaA ΔnhaR hns strain. The data from one representative experiment of five very similar independent repetitions are shown.