Engineering a Circular Riboregulator in Escherichia coli
Diagram of group I and PIE ribozymes [14, 18] and mechanism of riboregulation. (a) Left: secondary structure of wild-type group I intron, with the dispensable P6 loop colored in green, introns in pink, and exons in blue. Right: structure of the PIE ribozyme, with riboregulator RAJ31  inserted between the exons. (b) Sequence scheme in the wild-type group I ribozyme and illustration of products after self-splicing. (c) Sequence scheme in the PIE ribozyme, where the order of the introns and exons is inverted, and illustration of products after self-splicing, including the circularized sRNA. (d) Diagram of riboregulation with a circular sRNA. A cis-repressed mRNA is trans-activated by the circular sRNA, which induces a conformational change in the 5 UTR to release the RBS and then allow translation initiation (see sequences and structures of our design in Figures S1 and S2).