SAH riboswitches are a kind of riboswitch that bind S-adenosylhomocysteine (SAH).[1] When the coenzyme S-adenosylmethionine (SAM) is used in a methylation reaction, SAH is produced. SAH riboswitches typically up-regulate genes involved in recycling SAH to create more SAM (or the metabolically related methionine). This is particularly relevant to cells, because high levels of SAH can be toxic.[2] Originally identified by bioinformatics,[3] SAH riboswitches are apparent in many species of bacteria, predominantly certain Pseudomonadota and Actinomycetota. The atomic-resolution 3-dimensional structure of an SAH riboswitch has been solved using X-ray crystallography.[4]
Consensus secondary structure of SAH riboswitches. Layout is similar to that used in a published depiction.[1] Three base pairs in this secondary structure were incorrectly predicted, while an additional base pair is missing, as revealed by an atomic-resolution tertiary structure.[4]
