A targeting construct was designed to insert the nonsense mutation TAT>TAG at codon 1041 of the myosin IIIA (Myo3a) gene. This mutation, corresponding to human codon 1042, results in a stop codon in exon 28 commonly found in humans with adult on-set hearing loss DFNB30. Also, an ACN cassette was placed upstream of exon 28. The ACN cassette, containing the neomycin resistance gene and Cre recombinase gene under the control of angiotensin-converting enzyme promoter, is flanked by loxP sites. Cre-mediated recombination during spermatogenesis removed the cassette leaving one loxP site.