A targeting vector was designed to replace the seven coding exons the sulfotransferase 2B1 (Sult2b1) gene with a cassette containing the neomycin resistance gene and Cre recombinase gene under the control of angiotensin-converting enzyme promoter. This cassette was flanked by loxP sites. Cre-mediated recombination during spermatogenesis removed the inserted cassette leaving one loxP site. (J:186536)