Nucleotide insertion fidelity of human hepatitis B viral polymerase

The hepadnaviruses replicate their nucleic acid through a reverse transcription step. The MBP-fused HBV polymerase mas expressed in E. coli and purified by using amylose affinity column chromatography, The purified protein represented DNA-dependent DNA polymerase activity. In this report, the MBP-HBV polymerase was shown to lack 3'--> 5' exonuclease activity: Like other retroviral RTs, The ratio of the insertion efficiency for the wrong versus right base pairs indicates the misinsertion frequency (f). The nucleotide insertion fidelity (1/f), observed with the MBP-HBV polymerase and HIV-1 RT, was between 60 and 54,000, and between 50 and 73,000, respectively, showing that they are in close range. A relatively efficient nucleotide incorporation by the MBP-HBV polymerase was observed with a specificity of three groups: (1) A : T, T : A>C : G, G : C (matched pairs), (2) A: C, C : A>G : T, T : G (purine-pyrimidine and pyrimidine-purine mispairs), and (3) C:C, A:A, G:G, T: T>T: C, C: T>A: G, G:A (purine-purine or pyrimidine-pyrimidine mispairs), and their order is (1)>(2)>(3). The data from the nucleotide insertion fidelity by tbe MBP-HBV polymerase suggest that the HBV polymerase may be as error-prone as HIV-1 RT.