UASt regulatory sequences drive expression of the R2-element ORF (this encodes the R2 retrotransposase), tagged at the N-terminal end with 3xTag:FLAG. Silent mutations have been introduced into the coding sequence (CCGGTTGAACTCATCAATCAA to ACGTCTTAATAGCAGTATTAA) to render it resistant to RNAi-mediated knockdown by the P{UAS-R2(ORF).RNAi.1} transgene.