Figure 1.

RNA switches are RNAs that alter their structure in response to an input signal. In prokaryotes, the conformational change normally results in the creation or release of hairpin loops or similar structures that obstruct ribosome binding to the RBS. In the upper panel, the ribosome has easy access to the RBS, allowing for the translation of the protein (green ribbon). The binding of a small molecule (orange) to the RNA near the RBS causes a conformation change that obstructs ribosome binding and thus inhibits translation. In the lower panel, the natural conformation of the RNA obstructs ribosome binding. Complementary RNA (green) binds to the hairpin loop structure, exposing the RBS to the ribosome and thus permits translation. RBS, ribosome binding site; ORF, open reading frame.