Table 2.

Effect of various tryptophan concentrations on expression of trpE′-′lacZ fusions

StrainRelevant genotypeβ-Gal activityaβ-Gal ratioe
0 μMb20 μM50 μM100 μM200 μM400 μM0 μM/200 μM20 μM/400 μM
PLBS127WTtrpL 42 ± 11NDd NDND0.1 ± 0.02ND420ND
PLBS129SDtrpL 39 ± 9ND NDND5.3 ± 0.2ND7ND
PLBS176WT trpL trpC2 NAc 44 ± 127.4 ± 2.12.6 ± 0.20.8 ± 0.10.2 ± 0.06NA220
PLBS201SD trpL trpC2 NA 43 ± 1112 ± 1.08.7 ± 1.05.0 ± 0.44.7 ± 0.2NA9
  • a The β-galactosidase (β-Gal) activity expressed from the trpE′-′lacZ fusion is given in Miller units (21). The values are averages from at least three independent experiments ± standard deviation.

  • b Concentration of tryptophan in the growth media.

  • c NA, not applicable. Tryptophan auxotrophic strains require tryptophan for growth.

  • d ND, not determined.

  • e Ratio of activities at the indicated concentrations.