Gene targeting of the murine Abc1 gene. (A) Strategy to disrupt Abc1 expression. The targeting vector construct was designed to replace exons 17–22 that encode the first nucleotide-binding fold. The resulting targeted allele has pMC-neo replacing the six exons deleting an endogenous BamHI (B) site resulting in a restriction fragment length polymorphism, from 6.8 kb to 4.4 kb, with a downstream BamHI (B′) site by using an external 5′ probe. (B) Southern analysis of offspring from Abc1+/− matings. All three genotypes are observed by using the genomic probe strategy described above. Lanes A, C, and E, samples from +/+ mice; lanes B and D, samples from +/− mice; lanes F and G, samples from −/− mice. (C) RT-PCR results from Abc1+/+ and −/− mice. Lanes B and C are DNA and no DNA controls, respectively. Lane D is RT-PCR of hepatic RNA for Abc1 from wild-type mouse. Lane D is RT-PCR from Abc1−/− mice. Lane A is a 100-bp molecular weight marker.