FIG. 4.

Effect of replacement of guanines at the transcription initiation bases (positions 1 and 2) of the ptsGHI operon by adenine on negative stringent control of this operon. (A) The two guanines (GG) at the transcription initiation site (positions 1 and 2) of the ptsGHI promoter (nucleotides −55 to 26) were replaced by GA, AG, and AA, as described in Materials and Methods. The −35 and −10 regions of the ptsGHI promoter are underlined. (B) The mutant core ptsGHI promoters were placed upstream of lacZ in the relA⁺ and codY⁺ backgrounds. lacZ expression in the resulting strains (FU934 with GA, FU1042 with AG, and FU1045 with AA), as well as in strain FU906 with GG, was monitored upon lysine starvation and decoyinine treatment, as described in Materials and Methods. OD₆₀₀ values (small symbols) and LacZ activities (large symbols) are indicated by circles for FU906 with GG, by squares for FU1042 with AG, by triangles for FU934 with GA, and by diamonds for FU1045 with AA; filled and open symbols indicate results obtained with and without lysine starvation and decoyinine treatment, respectively. The arrows indicate the onset of the stresses.