Figure 1.

Design of the toehold switch riboregulator. The switch RNA is a functional mRNA whose translation is repressed by sequestering the RBS and start codon within a hairpin secondary structure. A cognate trigger RNA, which can adopt virtually any sequence in domains a* and b*, can initiate binding to the switch RNA through the single-stranded toehold domain and unwind the switch hairpin through hybridization with complementary domains a and b. The resulting trigger–switch complex has an exposed RBS and start codon enabling translation of the output gene.