OVERLAPPING INITIATOR AND TATA BOX FUNCTIONS IN THE BASAL CORE PROMOTER OF HEPATITIS-B VIRUS

The regulation of transcription of the hepatitis B virus core promoter is an important event in the viral life cycle. Two messages, precore and pregenomic RNAs, that are initiated 30 nucleotides apart are produ ced by the core promoter. Precore RNA encodes nucleocapsid protein and pregenomic RNA core and polymerase. The latter transcript also serves as a-template for viral genome replication via reverse transcription. We have previously defined a basal core promoter, which contains four TA-rich sequences (TA1 through TA4) but no canonical TATA element, th at can direct transcription of both messages. In this study, we demons trated that a stretch of 15 nucleotides containing TA4 is sufficient t o direct precise initiation of both precore and pregenomic transcripts . This sequence can function as both an initiator and a TATA element. Mutational analysis further revealed that sequences essential for eith er function are colocalized. The significance of this finding with res pect to the basal transcription mechanism and regulation of viral gene expression is discussed.