Riboswitches are highly structured, non-coding RNA elements located upstream of the coding region of bacterial mRNAs. They bind cellular ligands via their aptamer domain to regulate gene expression of the adjacent gene or operon through their expression platform domain. Five riboswitch classes have been identified that sense nucleotide-based signalling molecules, including c-di-GMP and c-di-AMP. This study describes a riboswitch class that selectively binds the alarmone guanosine tetraphosphate (ppGpp). Binding of ppGpp to candidate riboswitches induced structural changes in the RNA, and gene expression was regulated via transcription termination. Riboswitches for ppGpp may regulate genes involved in branched-chain amino acid biosynthesis, genes encoding glutamate synthase domains and operons containing ATP-binding cassette transporters.
Sherlock, M. E., Sudarsan, N. & Breaker, R. R. Riboswitches for the alarmone ppGpp expand the collection of RNA-based signaling systems. Proc. Natl Acad. Sci. https://doi.org/10.1073/pnas.1720406115 (2018)
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Du Toit, A. ppGpp triggers the switch. Nat Rev Microbiol 16, 454 (2018). https://doi.org/10.1038/s41579-018-0042-z