Thiostrepton is a highly modified multicyclic peptide antibiotic synthesized by diverse bacteria. Although best known as an inhibitor of protein synthesis, thiostrepton is also a potent activator of gene expression in Streptomyces lividans. In these studies, we characterize the nature of the
Microbial metabolites isolated in screening programs for their ability to activate transcription of the tipA promoter (ptipA) in Streptomyces lividans define a class of cyclic thiopeptide antibiotics having dehydroalanine side chains ("tails"). Here we show that such compounds of heterogeneous