The targeting event replaced 4.2 kb of DNA containing exons 3, 4 and 5 with a neomycin resistance (PGK-neo ) cassette. Northern and western blot analyses verified that mRNA and protein encoded by the targeted gene are both absent in tissues of homozygous mutant mice. Microarray analysis revealed a small (~30% +/- 10%) but statistically significant increase in Car13 transcript levels in mice lacking CAR3. (J:94222)