INTERACTION OF TRANSCRIPTION FACTORS RFX1 AND MIBP1 WITH THE GAMMA-MOTIF OF THE NEGATIVE REGULATORY ELEMENT OF THE HEPATITIS-B VIRUS CORE PROMOTER

The negative regulatory element (NRE) of the hepatitis B virus (HBV) c ore promoter contains three subregions which act synergistically to su ppress core promoter activity. One of these subregions, NRE gamma is a ctive in both HeLa cervical carcinoma cells and Huh7 hepatoma cells an d was found to be bound by a protein factor present in both cell types . Here we show that the transcription factor RFX1 can bind to NRE gamm a and transactivate the core promoter through this site. Mutations whi ch abrogated the gene-suppressive activity of NRE gamma prevented RFX1 from binding to NRE gamma. In addition, RFX1 can bind simultaneously, most likely as a heterodimer, with the transcription factor MIBP1 to NRE gamma. In the absence of a cloned MIBP1 gene for further studies, we hypothesize that RFX1 acts with MIBP1 to negatively regulate the co re promoter activity through the NRE gamma site. The ability of RFX1 t o transactivate the core promoter raises the possibility that RFX1 may play a dual role in regulating HBV gene expression. (C) 1997 Academic Press