FIGURE 1.

The absence of GrlR derepresses the expression of locus of enterocyte effacement (LEE) operons under repressing conditions. (A) The transcriptional activity of the LEE1-cat, LEE2-cat, LEE4-cat, LEE5-cat, and dnaK-cat fusions was analyzed in WT EPEC (black bars) and its ΔgrlR isogenic mutant (white bars), grown in 50 ml DMEM (D) or LB medium (L) with shaking at 37°C. Specific chloramphenicol acetyltransferase (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 < 0.01; ^***p-value < 0.001; ^****p-value < 0.0001). (B) Profile of secreted proteins of EPEC WT, Δler and ΔgrlR (carrying the empty vector pMPM-T3 or its derivative pT3GrlR) grown under the same conditions as in panel (A). Secreted proteins were concentrated from culture supernatants by precipitation with trichloroacetic acid (TCA) and separated by 12% SDS-PAGE. V: pMPM-T3, R: pT3GrlR.