Symbol SAM_alpha RNA type Cis-reg; riboswitch GO 0045814 | Rfam RF00521 Domain(s) Bacteria SO 0000035 | |
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The SAM-II riboswitch is a RNA element found predominantly in alpha-proteobacteria that binds S-adenosyl methionine (SAM). 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. Also, like many structured RNAs, SAM-II riboswitches can tolerate long loops between their stems.
Structure
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.