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). Multiple mutations have also been introduced into the osk 3'UTR sequence; these disrupt a subset of the pyrimidine tract sequences in the UTR.