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The SAM-II riboswitch is an RNA element found predominantly in Alphaproteobacteria that binds S-adenosyl methionine (SAM).[1] Its structure and sequence appear to be unrelated to the SAM riboswitch found in Gram-positive bacteria. This SAM riboswitch is located upstream of the metA and metC genes in Agrobacterium tumefaciens, and other methionine and SAM biosynthesis genes in other alpha-proteobacteria. Like the other SAM riboswitch, it probably functions to turn off expression of these genes in response to elevated SAM levels. A significant variant of SAM-II riboswitches was found in Pelagibacter ubique and related marine bacteria and called SAM-V.[2] Also, like many structured RNAs, SAM-II riboswitches can tolerate long loops between their stems.[3]
| SAM riboswitch (alpha-proteobacteria) | |
|---|---|
 Predicted secondary structure and sequence conservation of SAM_alpha | |
| Identifiers | |
| Symbol | SAM_alpha |
| Rfam | RF00521 |
| Other data | |
| RNA type | Cis-reg; riboswitch |
| Domain(s) | Bacteria |
| GO | GO:0045814 |
| SO | SO:0000035 |
| PDB structures | PDBe |
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The SAM-II riboswitch is short with less than 70 nucleotides and is structurally relatively simple being composed of a single hairpin and a pseudoknot.
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