FIGURE 4.

GrlR and H-NS repress locus of enterocyte effacement (LEE) gene expression by an indirect cooperative mechanism. (A) chloramphenicol acetyltransferase (CAT) activity of the LEE2-cat fusion was determined in WT enteropathogenic Escherichia coli (EPEC) and its Δler, Δhns, ΔgrlR, ΔgrlA, ΔgrlRA, ΔgrlRΔler, and ΔgrlRΔhns derivative mutants grown in 50 ml of Dulbecco’s modified Eagle’s medium (DMEM) (black bars) or Lysogeny Broth (LB) (white bars) with shaking at 37°C. Specific CAT activity was determined from samples collected at an OD₆₀₀ of 1. Values are an average of three independent experiments performed in duplicate. Error bars indicate standard deviations. Statistically different values are indicated (*p-value < 0.1; ^**p-value < 0.01; ^***p-value < 0.001; ^****p-value < 0.0001). (B) Secreted proteins of the same cultures were concentrated from supernatants by precipitation with TCA, separated by 12% SDS-PAGE and stained with Coomassie brilliant blue.