Targeting the Bc and βIL-3 loci.
(A) Partial map of the Bc locus, targeting construct, and predicted alteration of the Bclocus after homologous recombination. Coding exons are numbered and shown as black boxes. Noncoding exons are shaded gray. The position of probe A is indicated. This probe was used to identify homologous recombinants and to genotype mice by Southern blotting. Restriction enzyme sites are shown, where B indicates BamHI; E,EcoRI; S, SacI; V,EcoRV. (B) Southern blot analysis of tail DNA from offspring of a chimera generated by injection of ES cells containing targeted mutations of the Bc and BIL3 loci. DNA was digested with BamHI. Blots were probed with probe A (top panel) or a probe that detects the targeted mutation of theBIL3 locus (bottom panel).8 In the top panel, the targeted Bc allele is a 6.7-kb (kilobase) band, and the wild type allele is a 5-kb band. The probe cross-hybridizes with the BIL3 locus, which is seen as a 10-kb band. In the bottom panel, the 9-kb band represents hybridization of the probe to the Bcand BIL3 wild type alleles. The targeted BIL3 allele is seen as a 2.5-kb band. In the ES cell line used to generate these mice, the targeted mutations in the Bc and BIL3 loci are always observed in the same offspring, indicating that the homologous recombination events in the 2 loci lie on the same chromosome.
