Two SAM riboswitches in Bacillus subtilis that were experimentally studied act at the level of transcription termination control.

[6] The SAM riboswitch is organized about a four way junction, with two sets of coaxially stacked helices arranged side-by-side.

The methyl group is recognized indirectly through the charged sulfur, which forms an electrostatic interaction with the negative surface potential created by the tandem AU pairs in the minor groove of P1.

[citation needed] Affinity for SAH, however, is unaffected by changes to the P1 sequence, further supporting the idea that the interaction between SAM and the P1 helix is electrostatic in nature.

The variant riboswitches lack an internal loop that might allow such a turn, and also show no signs of forming the SAM-I–like pseudoknot.