FLP-mediated recombination between the two progenitor insertions (PBac{WH}E2f1f05222 and P{XP}E2f1d01508) has deleted the intervening genomic sequence, removing the exon that encodes the 5'UTR of the E2f1 RA, RD and RE isoforms; the deletion extends from 35bp upstream to 2857bp downstream of the RA/RE isoform transcription start site. A hybrid residual element remains at the site of the deletion.