The metA RNA element. (a) Sequence alignment of representative metA RNAs. Shaded nucleotides represent conserved base pairing regions. Lowercase and uppercase letters in the consensus line indicate 80% and 95% sequence conservation, respectively. A complete alignment is available in Additional data file 1. Organism abbreviations: Atu, Agrobacterium tumefaciens; Bja, Bradyrhizobium japonicum; Bme, Brucella melitensis; Mma, Magnetospirillum magnetotacticum; Mlo, Mesorhizobium loti; Rsp, Rhodobacter sphaeroides; Rpa, Rhodopseudomonas palustris; Sme, Sinorhizobium meliloti; Cbu, Coxiella burnetii; Bth, Bacteroides thetaiotaomicron; Bbr, Bordetella bronchiseptica. (b) Consensus sequence and structure of the SAM-I riboswitch aptamer found in Gram-positive bacteria. The consensus is updated from  and depicted using the same conventions as Figure 1a. The SAM-II aptamer structure is shown for comparison. (c) Comparison of genes in the methionine and SAM biosynthetic pathways found downstream of SAM-I and SAM-II riboswitches.