A neomycin resistance gene replaced the 472-nucleotide protein-coding region of exons 1-4 via homologous recombination. Immunoblot analysis of testicular extracts confirmed absence of both the ~60-kDa precursor (ACRBP-W) and the variant (ACRBP-V5) protein forms, as well as the ~32-kDA ACRBP-C form which is posttranslationally produced from ACRBP-W during spermatogenesis.