Promoter-specific inhibition of transcription by antibiotics which act on DNA gyrase.

Nalidixic acid, novobiocin and coumermycin specifically inhibit phage promoter-dependent transcription of the trp operon in phi 80 ptrp but not transcription from the authentic trp promoter. The nalidixic acid inhibition is not observed in an E. coli strain containing a nalAr mutation. These results indicate that DNA gyrase is involved in transcription.