UAS regulatory sequences drive expression of a reporter in which two coding sequences (rLUC and GFP-tagged pLUC) are separated by a kel gene test fragment that extends from 84 nucleotides 5' to 99 nucleotides 3' relative to the UGA kel ORF1 stop codon and in which the UGA codon has been mutated to an in-frame UGG. Designed to be used a control in an assay to test the ability of the kel fragment to mediate stop codon readthrough; readthrough efficiency can be calculated from the ratio of GFP produced by P{UAS-rLUC-UGA-99-fLUC::GFP} relative to this control construct.