In order to increase achievable library size during directed evolution, we aimed to harness the mutagenic capacity of Ty1 reverse transcriptase. Specifically, we inserted the URA3 gene into a galactose-activated Ty1 retrotransposon in the reverse orientation relative to Ty1 transcription, and transformed a plasmid containing this construct into S. cerevisiae BY4741. Then, by next-generation sequencing of a PCR-amplified locus of the URA3 gene after incubation with either glucose or galactose, we were able to measure conferred error rate by Ty1RT in this system.