uORF‐mediated riboregulation controls transcription of whiB7/wblC antibiotic resistance gene

WhiB7/WblC is a transcriptional factor of actinomycetes conferring intrinsic resistance to multiple translation‐inhibitory antibiotics. It positively autoregulates its own transcription in response to the same antibiotics. The presence of a uORF and a potential Rho‐independent transcription terminator in the 5′ leader region has suggested a possibility that the whiB7/wblC gene is regulated via a uORF‐mediated transcription attenuation. However, experimental evidence for the molecular mechanism to explain how antibiotic stress suppresses the attenuator, if any, and induces transcription of the whiB7/wblC gene has been lacking. Here we report that the 5′ leader sequences of the whiB7/wblC genes in sub‐clades of actinomycetes include conserved antiterminator RNA structures. We confirmed that the putative antiterminator in the whiB7/wblC leader sequences of both Streptomyces and Mycobacterium indeed suppresses Rho‐independent transcription terminator and facilitates transcription readthrough, which is required for WhiB7/WblC‐mediated antibiotic resistance. The antibiotic‐mediated suppression of the attenuator can be recapitulated by amino acid starvation, indicating that translational inhibition of uORF by multiple signals is a key to induce whiB7/wblC expression. Our findings of a mechanism leading to intrinsic antibiotic resistance could provide an alternative to treat drug‐resistant mycobacteria. In Streptomyces coelicolor and Mycobacterium smegmatis, antibiotic‐responsive induction of the whiB7/wblC intrinsic resistance gene is mediated, in part, via its 5′ leader region harboring uORF and the Rho‐independent terminator (RIT). An exposure to antibiotic inhibiting uORF translation liberates an antiterminator, previously occupied by uORF‐translating ribosome. The formation of the antiterminator suppresses RIT formation, thus promoting transcription elongation into the whiB7/wblC gene in the presence of translation‐targeting antibiotics.