Fig. 2.

Transcription of the pheA leader under amino acid stress is reduced in the absence of quality control by PheRS editing. β-Galactosidase activity from an E. coli pheA leader-lacZ expression transcriptional reporter was monitored in wild-type PheT and editing-defective PheT(G318W) strains. β-Gal activity is reported as rate (Δ absorbance at 420 nm time) as a function of OD₆₀₀ and was determined for both wild-type PheT (solid bars) and PheT(G318W) (checkered bars) strains at late log phase. Activity from cultures grown in M9 minimal medium containing no Phe, 50 µM and 100 µM Phe, and 4 µM and 10 µM m-Tyr are shown. Error bars represent the SD from three independent experiments.