FIG. 8.

Effect of replacement of adenine at each of the transcription initiation bases (position 1) of the pycA (left panel) and alsSD (right panel) operons by guanine on positive stringent control. The adenine at the transcription initiation site (+1) of the pycA and alsSD promoters (nucleotides −55 to 26) was replaced by guanine. The mutant pycA and alsSD promoters were placed upstream of lacZ in the relA⁺ and codY⁺ background. lacZ expression in wild-type strains FU977 (pycA) and FU937 (alsSD) and mutant strains FU1060 (pycA mutant) and FU1061 (alsSD mutant) was monitored upon decoyinine treatment, as described in Materials and Methods. OD₆₀₀ values (small symbols) and LacZ activities (large symbols) are indicated by circles for FU977 and FU937 and by squares for FU1060 and FU1061; filled and open symbols indicate results obtained with and without decoyinine treatment, respectively. The arrows indicate the onset of decoyinine treatment.