Hepatitis B virus preS1 functions as a transcriptional activation domain.

Hepatitis B virus (HBV) preS1 fused to the GAL4 DNA-binding domain functioned as a transcriptional activation domain in yeast and mammalian cells. The GAL4-preS1 fusion proteins derived from the preS1 of all three tested HBV subtypes (adr, adw and ayw) specifically activated the transcription of a lacZ or chloramphenicol acetyltransferase reporter gene linked to a GAL4-responsive promoter in transient transfection assays using yeast or HepG2 cells, respectively. Deletion analyses showed that the segments of preS1 from residues 21 to 90 and from residues 21 to 56 are sufficient and essential for the activity, respectively. Stable expression of GAL4-preS1 in Chinese hamster ovary cells also produced transactivator activity. These results suggest that preS1 fused to any DNA-binding domain of transcription factors would have transactivation potential.