An FRT cassette (containing y+t7.7 and Rnor\Cd2 sequences) separates UAS sequences from a Delta coding region in which the intracellular domain has been replaced by sequence encoding a ubiquitin moiety in which all 7 Lys residues have been mutated to Arg (to avoid additional ubiquitination). The Delta coding sequence is tagged with six tandem copies of Tag:MYC (the tag sequence is inserted in the extracellular domain, 17 residues upstream of the transmembrane domain).