532 nucleotides of the gene spanning exons 10-12 were replaced with a neomycin resistance cassette via homologous recombination resulting in a deletion and frameshift. RT-PCR verified the presence of mutant transcript in brain of homozygous mutant animals. Disruption of protein function was verified via ascorbic-acid uptake assay. Mouse embryonic fibroblasts from homozygous mutant animals exhibit less than 5% of normal ascorbic-acid uptake compared to wild-type. (J:76194)