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y+t7.7 and Rnor\Cd2 sequences) separates UAS sequences from a Delta coding region in which the intracellular domain has been replaced by sequence encoding a ubiquitin moiety in which all 7 Lys residues have been mutated to Arg (to avoid additional ubiquitination) and in which the Ile residue at position 44 has been mutated to Ala (this inactivates the internalization signal). 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).