Exon 91 of the perlecan gene was first replaced by a loxP flanked neo cassette by homologous recombination. The cassette was then removed by breeding with a mouse carrying the Cre recombinase. Since the reading frame is not altered by the deletion, a protein lacking 19 amino acids is produced. The deletion leads to loss of the C-terminal glycosaminoglycan attachment site. (J:82809)