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.

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] 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.