Interaction between hepatitis B virus core protein and reverse transcriptase

Previous mutagenesis studies with hepatitis B virus (HBV) suggest that continued interactions with core are required for several steps in genomic replication. To examine core-polymerase (Pot) interactions, insect cells were coinfected with baculovirus constructs that independently expressed core and Pot. The results demonstrated several features with implications that core plays an interactive role with HBV Pot: (i) core coprecipitated with constructs expressing full-length Pol as well as the terminal protein (TP), reverse transcriptase (RT) and RNase H domains of Pot, independently; (ii) coprecipitation of core was not dependent on the presence of an epsilon stem-loop sequence; and (iii) core-Pol complexes migrated as intact capsid particles, as detected by sucrose gradient analysis. To analyze the structural and sequence requirements of core in recognition of Pot, a series of core mutants with two- to four-amino-acid insertions or carboxy-terminal deletions were assessed for Pot interaction. The results indicated that capsid formation is required but not sufficient for interaction with Pot and that the TP and RT domains of Pot have different requirements for interaction with core. To map the core binding sites on Pot, a panel of amino- and carboxy-terminal deletion mutants of the TP and RT domains of Pot were analyzed for interaction with core. At least three separate core binding sites on Pot were detected. This analysis begins to define basic requirements for core-Pol interactions, but further study is necessary to delineate the effects of these interactions on encapsidation and genome replication.