A 4.5 kb region of the gene spanning exons 9 and 10 encoding the ATPase domain was replaced with a IRES-lacZ-PGK-neo cassette via homologous recombination. No gene transcripts were detected by RT-PCR analysis using primers amplifying exon 8 or 11, and Western blot analysis showed complete absence of protein product from testes of homozygous mutants. (J:61665)