Hepatitis B virus: DNA polymerase activity of deletion mutants

The hepadnavirus P gene product is a multifunctional protein with priming, DNA- and RNA-dependent DNA polymerase, and RNase H activities. Nested N- or C-terminal deletion mutations and deletions of domain(s) in human HBV poly merase have been made. Wild-type and deletion forms of MBP-fused HBV polyme rase were expressed in E. coli, purified by amylose column chromatography, and the DNA-dependent DNA polymerase activities of the purified proteins we re compared. Deletion of the terminal protein or spacer regions reduced enz yme activity to 70%, respectively. However, deletion of the RNase H domain affected polymerase activity more than that of the terminal protein or spac er region. The polymerase domain alone or the N-terminal deletion of the po lymerase domain still exhibited enzymatic activity. In this report, it is d emonstrated that the minimal domain for the polymerizing activity of the HB V polymerase is smaller than the polymerase domain.