Inhibition of RNA- and DNA-dependent duck hepatitis B virus DNA polymerase activity by nucleoside and pyrophosphate analogs.

The DNA polymerase of hepadnaviruses has two different functions during virus replication. It acts both as an RNA-dependent DNA polymerase (reverse transcriptase) and as a DNA-dependent DNA polymerase. Duck hepatitis B virus (DHBV) preparations were used to investigate the inhibitory effects of selected compounds on these two enzyme activities. The reverse transcriptase activity was represented by an actinomycin D-resistant, phosphonoformate-sensitive DNA polymerase activity isolated from DHBV-infected duck livers. DHBV from serum was used as the source of the DNA-dependent DNA polymerase activity. Pyrophosphate and nucleoside triphosphate analogs were assayed for their inhibitory effects on the two enzyme preparations. A marked inhibition was obtained with 3'-fluoro-2',3'-dideoxythymidine 5'-triphosphate, acyclovir triphosphate, 2',3'-dideoxythymidine 5'-triphosphate, 2',3'-dideoxyguanosine 5'-triphosphate and 2',3'-dideoxythymidine 5'-triphosphate. The two thymidine analog triphosphates showed a markedly lower inhibitory effect on the reverse transcriptase activity than on the DNA-dependent DNA polymerase activity. This was in analogy with earlier findings with 3'-azido-2',3'-dideoxythymidine 5'-triphosphate. Among the tested pyrophosphate analogs only phosphonoformate was inhibitory.