IN-VIVO ACTIVITY OF THE HEPATITIS-B VIRUS CORE PROMOTER - TISSUE-SPECIFICITY AND TEMPORAL REGULATION

The contribution of the hepatitis B virus enhancers I and Il in the re gulation of the activity of the core and the X promoters was assessed in transgenic mice. Surprisingly, despite the presence of heterologous promoters linked 5' of the X gene, the transgene expression is mostly due to core promoter (Cp) activity present in the X coding sequence. Moreover, the restriction of Cp activity to hepatic tissue required th e combined action of both enhancers I and II, whereas the proximity of these two enhancers was insufficient to confer tissue specificity on Xp activity. Furthermore, the liver-specific activity of the Cp was de velopmentally regulated in an enhancer I-independent manner.