Exon 7 encoding putative transmembrane domains 7-9 and flanking intronic sequences were replaced with a PGK-hygro cassette in the reverse orientation via homologous recombination. Northern blot analysis did not detect gene expression in liver or kidney of homozygous mutant animals. However, RNase protection assay using a probe to nucleotides 447 to 691 lying outside the deleted region detected extremely low levels of transcript, which may represent a truncated and unstable message. Western blot analysis of homozygous mutant liver and kidney samples using a polyclonal antibody probe recognizing the C-terminal region of rat and mouse protein further verified the absence of gene expression. (J:70604)