Fig. 4.

Activity of E. coli FNR proteins with substitutions at residue 24. Plasmid pGS24 was subjected to QuikChange site-directed mutagenesis (Stratagene), and the plasmids expressing the indicated FNR variants were introduced to JRG1728 (fnr lac) containing pFF-41.5, a plasmid with an FNR-activated promoter fused to lacZ. Cultures were grown in L broth either aerobically (filled bars) or anaerobically (open bars). The mean β-galactosidase activities in MU ± SD are shown (n = 9). The horizontal lines indicate the amount of aerobic activity associated with overproduced wild-type FNR (Ser-24) and FNR-S24F.