FIG. 2.

Promoter truncation analysis at ctx. (A) Schematic representations of the extent of the ctx promoter present in each fusion construct are shown to the left. Gray rectangles each represent one reiteration of the heptad repeat 5′-TTTTGAT-3′. Culture of E. coli strains that are either hns⁺ or hns deficient (hns651) and carry a chromosomal copy of each fusion construct were grown to mid-log phase in LB medium at 30°C with shaking and assayed for β-galactosidase production. Data are expressed in Miller units and the standard deviation. The fold derepression was calculated as the increase in β-galatosidase activity in the hns-deficient strain compared to the hns⁺ strain. (B and C) DIG-labeled ctx promoter fragments from −522 to −178 (CU), −202 to + 114 (C2), −118 to + 114 (C3), and −65 to + 114 (C4). Fragments were incubated with purified H-NS and analyzed on a nondenaturing polyacrylamide gel. The first lane in each set has no protein added, the second lane contains 180 nM H-NS, and the third lane contains 360 nM H-NS.