Abstract
We report the successful transfer of a fully functional lac operator-repressor gene regulatory system to the mouse. The key component is a lac repressor transgene that resembles a typical mammalian gene both in codon usage and structure and expresses functional levels of repressor protein in the animal. We used the repressor to regulate the expression of a mammalian reporter gene consisting of the tyrosinase promoter embedded with three short lac operator sequences and the tyrosinase coding sequence. Pigmentation of the mouse was controlled by the interaction of the lac repressor with the regulatable Tyrosinase transgene in a manner that was fully reversible by the lactose analog IPTG. Direct control of mammalian promoters by the lac repressor provides tight, reversible regulation, predictable levels of de-repressed expression, and the promise of reversible control of the endogenous genome.