The SAM-II riboswitch, also known as SAM-alpha, was found so far only in alpha-proteobacteria. This riboswitch is one of several riboswitches that recognize S-adenosylmethionine (SAM) as a ligand, and regulates the methionine metabolism [16086852]. SAM is a common co-substrate involved in methyl group transfers and is synthesized from the methionine amino acid by the SAM synthase MetK. The SAM-II riboswitch located upstream of the methionine biosynthesis gene metA in Agrobac-terium tumefaciens was validated by in-line probing assays and the proof of direct binding between SAM and the SAM-II leader RNA was obtained [16086852].