A mutant human cDNA coding for the transmembrane and cytoplasmic domains of the receptor was inserted in-frame into mouse genomic sequences. The mutations resulted in alteration of a multifunctional tyrosinase motif from Y1349VHVNATY1356VNV to Y1349VNVNATY1356VNV. A floxed neo included in the construct was excised by crossing with Cre deleter mice. (J:94030)