FIG. 1.

SoxRS response as determined by expression of the fpr lacZ fusion. (A) Strains lacking the indicated locus were grown aerobically in NB to an OD₆₅₀ of 0.3, divided, and induced (gray) or not (white) with 250 μM PQ. Cultures were shaken aerobically for 1 h, and β-galactosidase activity was measured. Data for strains expressing (solid bars) and lacking (striped bars) yggX are shown. (B) Strains were grown in the presence of ampicillin and assayed as described above. Strains lacked yggX and contained either the vector pET20b or apbC cloned into pET20b, as indicated. Solid bars depict expression without induction, and striped bars depict expression with induction by 250 μM PQ. (C) Schematic of the elements required for fpr expression. Neither apo-SoxR nor SoxR with a reduced cluster allows transcription of the fpr gene.