SAM-II riboswitch

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

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.

See also

• SAM-I riboswitch
• SAM-III riboswitch
• SAM-IV riboswitch
• SAM-V riboswitch
• SAM-VI riboswitch