FIG 3 .

Expression of the P₅AP gene is induced in response to exposure to penicillin or following acquisition of a nonsense mutation in stpA. Cultures were grown in BHI broth to mid-log phase, and penicillin was added at 12.5 µg/ml (one-half of the MIC). After 30 min, cells were harvested and frozen for RNA preparation. Expression levels of 16S rRNA and tufA were used as references. Error bars indicate the standard error of the mean for biological duplicates. Results are representative of two independent experiments. (A) Relative gene expression of P₅AP in ceftriaxone-susceptible double class A Pbp mutant CV571 in response to growth in penicillin. (B) Relative gene expression of P₅AP in the Cro1 and Cro2 mutants and of ceftriaxone-susceptible triple class A Pbp mutant CV598 in response to growth in penicillin. (C) Relative gene expression of P₅AP in the Cro2 mutant alone and transformed with the wild-type stpA-stk.