The tetracycline transactivator (tTA) coding sequence followed by an IRES and lacZ coding sequence such were inserted downstream of the promoter region such that the ATG codon of tTA was inserted at the initiation site. In addition a construct with the tTA responsive promoter (phcmv-1) driving expression of an F7 cDNA was inserted adjacent to the lacZ containing cassette and this was followed by a floxed neo cassette. This total construct replaced the entire coding sequence of the gene. Analysis indicates that protein activity in plasma from homozygotes is about 0.7% that of wild-type controls. Results indicate that tetracycline treatment does not significantly change expression.