Targeting the mouse HPRT locus with the human ferrochelatase promoter transgenes.

(A) To introduce ferrochelatase promoter genes 5′ of the HPRT locus, we designed HPRT targeting vectors that contained human ferrochelatase promoter fragments driving expression of the EGFP cDNA flanked 5′ and 3′, with HPRT sequences containing the HPRT promoter, and exons 1, 2, and 3. After electroporation, a homologous recombination event between the HPRT gene and the targeting vector reconstitutes the HPRT gene function, which allows for selection in HAT media, and introduces a single copy of the ferrochelatase promoter transgene into the genomic DNA. (B) EGFP reporter genes contain various fragments of the human ferrochelatase promoter.