Confirmation at the DNA and RNA level of correct targeting of the ₂-AP gene. (A) Southern blot analysis of tail-tip genomic DNA of littermates from intercrosses of heterozygous ₂-AP–deficient mice. The DNA was digested with KpnI and hybridized with a 3′ probe (probe C in ref 10). The 8-kb and 5-kb bands indicate the presence of the wild-type or mutant allele, respectively. WT, wild-type; HR, homologously recombined. (B) RT-PCR analysis of polyA RNA isolated from liver and kidney of ₂-AP^+/+ and ₂-AP^−/− mice. PCR products were generated using PCR primers annealing in the coding part of exon 10 of the murine ₂-AP gene (deleted in the disrupted allele), and were separated on a 1% agarose gel. PCR with wild type RT-cDNA yielded the expected 193-bp amplification product (lanes 3 and 5). The absence of signal with ₂-AP^−/− RT-cDNA (lanes 4 and 6) confirmed the inactivation of the ₂-AP gene. Lane 2 (C) represents a negative control PCR reaction performed without DNA template. The lower band present in all lanes represents dimers of the primers.