Sequence for the 2A self-cleaving peptide, a diphtheria toxin receptor (HBEGF/DTR) cDNA and a loxP site flanked neomycin resistance gene cassette were inserted immediately before the stop codon. The neo cassette was removed through subsequent cre-mediated recombination. This allele expresses the endogenous peptide and the inserted DTR peptide. (J:292580)