SAH riboswitch

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 Proteobacteria and Actinobacteria. 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]
S-adenosyl-L-homocysteine riboswitch
Predicted secondary structure and sequence conservation of SAH_riboswitch
Identifiers
SymbolSAH_riboswitch
RfamRF01057
Other data
RNA typeCis-reg; riboswitch
Domain(s)Bacteria
SO0005836
PDB structuresPDBe

References
  1. Wang JX, Lee ER, Morales DR, Lim J, Breaker RR (2008). "Riboswitches that Sense S-adenosylhomocysteine and Activate Genes Involved in Coenzyme Recycling". Mol. Cell. 29 (6): 691–702. doi:10.1016/j.molcel.2008.01.012. PMC 2712820. PMID 18374645.
  2. Ueland PM (1982). "Pharmacological and biochemical aspects of S-adenosylhomocysteine and S-adenosylhomocysteine hydrolase". Pharmacol. Rev. 34 (3): 223–253. PMID 6760211.
  3. Weinberg Z, Barrick JE, Yao Z, et al. (2007). "Identification of 22 candidate structured RNAs in bacteria using the CMfinder comparative genomics pipeline". Nucleic Acids Res. 35 (14): 4809–4819. doi:10.1093/nar/gkm487. PMC 1950547. PMID 17621584.
  4. Edwards AL, Reyes FE, Héroux A, Batey RT (September 2010). "Structural basis for recognition of S-adenosylhomocysteine by riboswitches". RNA. 16 (11): 2144–2155. doi:10.1261/rna.2341610. PMC 2957054. PMID 20864509.
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