FIG. 6.

Effects of Met box or MetR inactivation on methionine (A)- and homocysteine (B)-dependent regulation of metE transcription. Levels of luciferase activity (amount of Lux per OD₆₀₀ unit) from the UA159 wild-type (JIM8867 and JIM8870) and ΔmetR mutant (JIM8873) strains expressing the wild-type PmetE-lux fusion and the Met box mutant PmetE-lux fusion (ΔMet-boxes) were measured. (A) Cells were grown in M17 medium to early exponential phase (OD₆₀₀ of 0.2). Bacterial cultures were split in two, washed, and resuspended in CDM+C (⋄) or CDM+CM (⧫) (time zero). Cells were held in these media for 90 min, and luciferase activity was measured. (B) Cells were grown in CDM+CM to early exponential phase (OD₆₀₀ of 0.2). Bacterial cultures were split in two, and 4 mM homocysteine was added to one of the aliquots. The level of luciferase activity from cells cultivated in the presence (⧫) or in the absence (⋄) of 4 mM homocysteine was measured. The x axis shows the period of incubation after the addition of homocysteine (time zero). One curve representative of the results from at least three experiments is presented.