6S RNA, a Global Regulator of Transcription in Escherichia coli, Bacillus subtilis, and Beyond

6S RNA is a small, noncoding RNA that interacts with the primary holoenzyme form of RNA polymerase. Escherichia coli 6S RNA is a global regulator that downregulates transcription and is important for modulating stress and optimizing survival during nutrient limitation. Studies in diverse organisms suggest a higher complexity in function than previously appreciated. Some bacteria have multiple 6S RNAs that appear to have independent functions. 6S RNA accumulation profiles also are quite divergent and suggest they integrate into cellular networks in a species-specific manner. Nevertheless, in all tested systems the common theme is a role for 6S RNA in survival. Finally, there has been much excitement about the ability of 6S RNA to be used as a template to synthesize product RNAs (pRNAs). This review highlights the details of 6S RNA in Escherichia coli and compares and contrasts 6S RNAs in multiple species.