Abstract Hepatitis B virus (HBV) is a DNA virus which replicates
via reverse transcription. The structure and function of the
reverse transcriptase play important roles in HBV replication.
We have previously reported that when proline at residue 306
in HBV reverse transcriptase was substituted by other amino
acids, most of the mutants showed decreased replicative competency.
To explore the mechanisms for this decrease in replicative
competency, constructs with substituted amino acid residues at
rtP306 were used to transfect Huh-7 cells, and replication competencies,
transcription levels and encapsidation efficiencies of
the mutants and the parental viral strain were compared.
Decreased replication competency was found with many of the
mutants and confirmed by trans-complementation between each
mutant and a replication-defective replicon. No change in transcriptional
level was detected between all mutated constructs.
The encapsidation competencies of these constructs were studied
by assaying pregenomic RNAs in intracytoplamic core particles
from transfected cells, which were normalized for the amount of
HBV core protein by Western blotting using anti-core antibodies.
Impaired encapsidation was found in several mutants substituted
at residue 306, thereby demonstrating for the first time that
conservation of proline at this residue is crucial for efficient
encapsidation of pregenomic RNA.