UAS regulatory sequences are fused upstream of RpS20, including its native stop codon and extension 3'UTR. The coding sequence for NanoLuc (missing a start codon) has been inserted immediately upstream of the second in-frame stop codon in the extension 3'UTR. If translation terminates at the native RpS20 stop codon, the NanoLuc reporter is not translated. If translational readthrough occurs past the stop codon, the RpS20 protein produced is tagged with the NanoLuc reporter.