The pancreas-specific transcriptional enhancer of the rat elastase I gene was modified by
substituting, in turn, each of its three individual constitutive elements with the tetO element,
which confers regulation by exogenous tetracycline in the presence of the hybrid tetO
binding transactivator (tTA). Whereas the unmodified enhancer was active in transfected
acinar tumor cells, substitution of individual elements with the tet-responsive element
abolished activity. The modified enhancers were reactivated in the presence of the tTA and …