Riboswitch

Riboswitches are regulatory segments of an mRNA that bind small metabolites to control gene expression. They consist of two main parts: an aptamer domain that binds a specific ligand, and an expression platform that translates the binding event into a change in gene expression. Most riboswitches are located in the 5' untranslated region of the mRNA they regulate and control genes involved in the synthesis, transport, or metabolism of the ligand.

Mechanistically, riboswitches act through conformational changes in the mRNA. In the absence of the ligand, the transcript can adopt structures that allow transcription to continue or translation to begin. When the ligand binds the aptamer, the RNA folds into an alternative structure that typically either forms a transcription terminator hairpin, causing premature transcription termination, or sequesters the ribosome binding site, reducing translation. Some riboswitches influence mRNA stability or splicing, particularly in eukaryotes.

Riboswitches are widespread in bacteria and archaea and have also been found in some plants and fungi. They regulate a range of essential pathways by sensing metabolites such as vitamins and nucleotides. Well-characterized examples include the thiamine pyrophosphate (TPP) riboswitch, which responds to vitamin B1 derivatives; the glycine and lysine riboswitches; and the fluoride riboswitch, which detects fluoride ions.

Research into riboswitches has provided insights into RNA structure and gene regulation and has implications for synthetic biology and antimicrobial design, given their central role in metabolic regulation and their reliance on RNA-based control mechanisms.