A construct consisting of a floxed PGK-hygro cassette, wild-type exons 2 and 3, a third loxP site, and a mutant exon 2 and 3 cDNA resistant to subtilisin-like proprotein convertase cleavage due to removal of the cleavage motif. Cre-mediated recombination results in production of a cleavage resistant protein. (J:112799)