Genomic fragment including the complete osk coding sequence, with three copies of Tag:HA introduced after amino acid residue T140 (this is one codon after the start codon for the short isoform). A M139L amino acid substitution has been introduced into the coding sequence (this is the translation start codon for the short isoform, and the mutation prevents expression of this isoform). Three of the 13 copies of the IBE (UUUAY) sequence present in the osk 3'UTR (copies 11-13, the 'A' subset) have been mutated.