Locations and architecture of tandem TPP riboswitches. (A) TPP aptamers (encircled TPP) reside adjacent to each other in several bacteria upstream of operons usually carrying genes for TPP metabolism. (*) Lmes02000088 ORF, (**) Lmes02000087 ORF, (***) Lmes02000083 ORF. In some organisms, tenI is named thiE, and goxB is named dadA. See Fig. 2 for description of gene functions. (B) Arrangement of tandem aptamers and single expression platform (gray) of some glycine riboswitches. (U n ) Stretch of repetitive U residues that is characteristic of intrinsic transcription terminators (Gusarov and Nudler 1999; Yarnell and Roberts 1999). Base-pairing portions of terminator (blue lines). (C) Tandem SAM-AdoCbl riboswitch arrangement that permits control of gene expression by two different metabolites (Sudarsan et al. 2006). (D) Arrangement of tandem TPP riboswitches.
