A tetracycline responsive element (TRE), which consists of heptamerized tet operator (tetO) sequences, the binding sites of TetR, located upstream of a cytomegalovirus minimal promoter was fused to the rat Grm1 open reading frame. Grm1 is expressed upon binding of the tetracycline-controlled transactivator (tTA) protein to the promoter. (J:122536)