FIG. 6.

Effect of replacement of guanine at the transcription initiation base (+1) of the pdhABCD operon with adenine on the negative stringent control of this operon. (A) The guanine at the transcription initiation site (+1) of the pdhABCD promoter (nucleotides −47 to 167) was replaced by adenine. The −35 and −10 regions of the pdhABCD promoter are underlined. (B) The mutant pdhABCD promoter was placed upstream of lacZ in the relA⁺ and codY⁺ backgrounds. lacZ expression in the resulting strains (FU1019 [wild type] and FU1044 [mutant]) 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 FU1019 and by squares for FU1044; filled and open symbols indicate results obtained with and without lysine starvation and decoyinine treatment, respectively. The arrows indicate the onset of these stresses.