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y+t7.7 and Rnor\Cd2 sequences) separates UAS sequences from a Delta coding region in which the intracellular domain has been replaced by a random peptide of 50 residues (same sequence as in P{UAS(FRT.y+CD2.A902)Delta.R.MYC} except two Lys residues have been replaced with Arg). 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).