The endogenous locus was disrupted by the random insertion of a gene trap vector containing a splice acceptor site followed by Beta-geo and a polyadenylation signal into exon 8, which encodes the third Ig-motif. Sequencing identified a nonsense mutation 14 codons downstream of the vector insertion site. Protein was undetected in homozygous mutant mice by Western blot analysis of kidney extracts. (J:85162)