ACTIVATION OF THE HEPATITIS-B VIRUS-S PROMOTER BY TRANSCRIPTION FACTOR NF-Y VIA A CCAAT ELEMENT

The middle and small surface proteins of hepatitis B virus are transla ted from 5'-heterogeneous transcripts specified by the S promoter. We have generated a series of linker-substitution mutants that encompass the 130 base pairs comprising this promoter and measured the amount of transcripts and protein products synthesized from each mutant. The re sults confirm our previous finding that a CCAAT element is an importan t up-stream activating element for this promoter, as mutation of this element leads to a >20-fold decrease in promoter activity. in vitro bi nding assays showed that the cellular transcription factor NF-Y (CCAAT -binding factor) binds to this element, and expression of a dominant-n egative NF-Y subunit in transfected cells specifically reduced surface protein expression from the S promoter via the CCAAT element. In addi tion, two spl sites also contribute to S promoter activity by a total of approximately 6-fold. Therefore, the S promoter is activated by bot h NF-Y and Sp1, but more strongly by the former factor. (C) 1996 Acade mic Press, Inc.