A floxed inverted MC1-neo cassette was inserted upstream of exon 6 and a loxP site was inserted downstream of exon 7 via homologous recombination. Cre mediated recombination removed the neo cassette and exons 6 and 7. Western blot analysis confirmed the absence of full length protein expression from this allele; however expression of a C terminal fragment was detected. (J:181294)