The Secret to 6S: Regulating RNA polymerase by Ribo-sequestration

Summary Regulating transcription under different conditions is vital to all organisms. As Escherichia coli shifts from exponential to stationary growth, regulation of transcription is achieved in large part by the tight binding of 6S RNA to Eσ70, RNA polymerase with the σ70 specificity subunit. Ribo-sequestration of Eσ70 by 6S RNA serves to downregulate σ70-dependent transcription, which is needed for exponential growth. This facilitates transcription from promoters dependent on stationary phase sigma, σs. Previous work has suggested that the 6S RNA binding to Eσ70 simply mimics the Eσ70/promoter interaction. In this issue of Molecular Microbiology, Klocko and Wassarman demonstrate that many of the contacts between residues within σ70 region 4 and 6S RNA are distinct from those between region 4 and promoter DNA. Several residues that interact with 6S RNA are ones previously known to interact with protein activators of Eσ70. Their work adds 6S RNA to the growing list of factors that can regulate Eσ70 by interacting with region 4.