The human steroid sulfatase cDNA (with added HA tag sequences) is driven by tetracycline response elements (TRE) and a minimal CMV promoter. Downstream of the cDNA are SV40 poly(A) signal sequences. The gene is only expressed in a tetracycline/doxycycline controllable manner if mice containing this allele are crossed with mice containing a tTA or rtTA allele. (J:211206)