Tfr2 genomic targeting construct. (A) The Tfr2 locus, the targeting construct, and the 2 mutagenized alleles are illustrated. Exons 3 to 7 of the murine Tfr2 gene are shown as black boxes. The inactivation cassette is in gray. LoxP sites are shown as arrows. M167K mutation is highlighted. Recombination between LoxP 2 and 3 generates Tfr2 KI allele. Recombination between LoxP 1 and 3 produces Tfr2 KO allele. E indicates EcoRI restriction sites used for construct cloning and Southern blot analysis. Barred line represents Southern blot probe. (B) Southern blot analysis showing first electroporation results to obtain the full targeted clones (7.1-kb band) versus the WT cell DNA (10-kb band). (C) Southern blot showing KI (3.9-kb band) and KO clones (2.4-kb band) obtained from Cre electroporation.