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y+t7.7 and Rnor\Cd2 sequences) separates UAS sequences from a Delta coding region in which the intracellular domain has been replaced by a 21 amino acid peptide that contains the wild-type internalization signal (FDNPVY) from the Hsap\LDLR gene. 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).