Figure 1.

Riboswitch Regulation of mRNA Processing in Mammalian Cells. (a) Regulation of polyadenylation. In the absence of ligand, the polyadenylation site (PAS, orange) is bound by the polyadenylation complex (orange), which removes a downstream miRNA target site (miR-T, red) and adds a poly-A tail to enable expression. Ligand binding (purple) to an aptamer domain (blue) sequesters the PAS, blocking processing and promoting mRNA degradation by exonucleases and miRNA-induced silencing [66]. (b) Regulation of splicing by ligand-induced exon skipping. In the absence of ligand binding, an exon with a premature stop codon is spliced into the mRNA, preventing gene expression. Ligand binding sequesters spliceosome recognition elements such as the 3′ acceptor site (3′ SS, orange), promoting exon skipping and expression of a full-length, functional protein [68,69,70,71].