UASp regulatory sequences are fused upstream of three segments of osk DNA: a genomic BamHI-EcoRI fragment (starting just upstream of the transcription unit and containing the first eight codons), a cDNA EcoRI-MluI fragment (containing most of the coding region) and a genomic fragment from the MluI site to a synthetic BamHI site introduced just after the stop codon (containing the C-terminal part of the coding region and the final, small intron).