UASt sequences regulate expression of a Hsap\EWSR1::Hsap\FLI1 fusion protein, with the fusion breakpoints in exon 7 of Hsap\EWSR1 and exon 6 of Hsap\FLI1 (this 'type 1' fusion is found in approximately 60% of Ewing sarcoma patients in which a Hsap\EWSR1::Hsap\FLI1 fusion protein is the causative oncogene). In addition, a 69 amino acid peptide corresponding to the 69 C-terminal amino acids of the protein encoded by the M{UAS-EWSR1::FLI1.1FS} transgene has been added to the C-terminal end of the fusion protein.