High-Throughput Quantitation of Yeast uORF Regulatory Impacts Using FACS-uORF

Eukaryotic upstream Open Reading Frames (uORFs) are short translated regions found in many transcript leaders (Barbosa et al. PLoS Genet 9:e1003529, 2013; Zhang et al. Trends Biochem Sci 44:782-794, 2019). Modern transcript annotations and ribosome profiling studies have found thousands of AUG-initiated uORFs, and many more uORFs initiated by near-cognate codons (CUG, GUG, UUG, etc.). Their translation generally decreases the expression of the main encoded protein by preventing ribosomes from reaching the main ORF of each gene, and by inducing nonsense mediated decay (NMD) through premature termination. Under many cellular stresses, uORF containing transcripts are de-repressed due to decreased translation initiation (Young et al. J Biol Chem 291:16927-16935, 2016). Traditional experimental evaluation of uORFs involves comparing expression from matched uORF-containing and start-codon mutated transcript leader reporter plasmids. This tedious process has precluded analysis of large numbers of uORFs. We recently used FACS-uORF to simultaneously assay thousands of yeast uORFs in order to evaluate the impact of codon usage on their functions (Lin et al. Nucleic Acids Res 2:1-10, 2019). Here, we provide a step-by-step protocol for this assay.