The peptide antibiotic gramicidin D. A specific reactivator of tyrocidine-inhibited transcription.

The sporulating bacterial strain Bacillus brevis (ATCC 8185) produces two types of peptide antibiotics, the linear gramicidins and the cyclic tyrocidines. Their effects on transcription in vitro were studied: 1. RNA synthesis catalized by RNA polymerase and DNA as template, both from B. brevis cells, is inhibited by the addition of gramicidin maximally to 50% as compared to controls without gramicidin. This inhibition is dependent on the concentration of gramicidin as well as on that of RNA polymerase. 2. Transcription of DNA is also inhibited by tyrocidine. This inhibition is partially compensated by the addition of gramicidin. Here, the action of gramicidin is again dependent on its concentration and on that of RNA polymerase. 3. This counteraction of gramicidin occurs only with RNA polymerase from B. brevis. Enzyme preparations of other origin are additively inhibited by gramicidin when previously inhibited by tyrocidine. The specific action pattern of gramicidin and tyrocidine in connection with the B. brevis RNA polymerase supports the notion that the two peptide antibiotics may be involved in a gene regulatory mechanism during sporogenesis.