Gene targeting strategy. (Top) Genomic clone containing exons 2-5 of Nrf-2 in EMBL3. Restriction sites indicated are Hind III (H) and Cla I (C). The exon 2 probe used to screen Southern blots is shown by a black box. The junction (J) with vector sequences (wavy lines) is shown, as is the germline Hind III fragment detected with the exon 2 probe. (Middle) Targeting vector showing insertion of the Neomycin resistance gene (Neo) into the fifth exon, in the reverse orientation relative to Nrf-2. An inactivated Hind III site is indicated by parentheses. The thymidine kinase gene (tk) is also in reverse orientation and lies outside the region of homology. (Bottom) Structure of the targeted allele after homologous recombination. The thymidine kinase gene has been lost as a result of homologous recombination. A rearranged 5.8-kb Hind III fragment is shown.