A cassette containing a single-chain reverse tetracycline-controlled trans-silencer (sc rtTS), a tetracycline-controlled transactivator (tTA), and a tetracycline responsive element (TRE) were introduced upstream of the translation start site in exon 2. The sc rtTS consists of two silencer moieties connected via a 36 amino acid linker. In the presence of doxycycline, the sc rtTS binds to tetO to suppress leaky expression of the locus. (J:104881, J:106458)