Artificial Protein-Responsive Riboswitches Upregulate Non-AUG Translation Initiation in Yeast

Artificial control of gene expression is one of the core technologies for engineering biological systems. Riboswitches are cis-acting elements on mRNA that regulate gene expression in a ligand-dependent manner often seen in prokaryotes, but rarely in eukaryotes. Because of the poor variety of such elements available in eukaryotic systems, the number of artificially engineered eukaryotic riboswitches, especially of the upregulation type, is still limited. Here, we developed a design principle for upregulation-type riboswitches that utilize non-AUG initiation induced by ribosomal stalling in a ligand-dependent manner in Saccharomyces cerevisiae. Our design principle simply required the proper positioning of a near-cognate start codon relative to the RNA aptamer. Intriguingly, the CUG codon was the most preferable for non-AUG ON switches in terms of output level and switch performance. This work establishes novel choices for artificial genetic control in eukaryotes with versatile potential for industrial and biomedical applications as well as basic research.