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Open Access Research article

Evidence that the RNAseH activity of the duck hepatitis B virus is unable to act on exogenous substrates

Yunhao Gong2, Ermei Yao1 and John E Tavis1*

Author Affiliations

1 Department of Molecular Microbiology and Immunology, St. Louis University School of Medicine, 1402 South Grand Blvd., St. Louis, MO 63104, USA

2 Viridae Clinical Sciences, 1134 Burrard St., Vancouver, B.C. V6Z 1Y8, Canada

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BMC Microbiology 2001, 1:12  doi:10.1186/1471-2180-1-12

Published: 19 July 2001

Abstract

Background

The hepadnaviral reverse transcriptase can synthesize DNA on its native RNA template within viral cores but it is usually unable to synthesize DNA employing exogenous nucleic acids as a template. The mechanism of this template commitment is unknown. Here we provide evidence that the RNAseH activity of duck hepatitis B virus reverse transcriptase may also be unable to act on exogenous substrates.

Results

RNAseH assays were performed under a wide variety of conditions employing substrate RNAs of Duck Hepatitis B Virus sequence annealed to complementary DNA oligonucleotides and permeabilized intracellular viral core particles. Temperature, pH, cation type, salt concentration, substrate concentration, and the sequences of the cleavage sites were varied, and the effects of ATP and dNTPs on RNAseH activity were examined. duck hepatitis B virus RNAseH activity was not detected under any of these conditions, although E. coli or Avian Myeloblastosis Virus RNAseH activity could be detected under all conditions. Access of the RNA substrate to the enzyme within the viral cores was confirmed.

Conclusions

These results imply that the RNAseH activity of the DHBV reverse transcriptase may not be able to degrade exogenous RNA:DNA heteroduplexes, although it can degrade heteroduplexes of the same sequence generated during reverse transcription of the endogenous RNA template. Therefore, the RNAseH activity appears to be "substrate committed" in a manner similar to the template commitment observed for the DNA polymerase activity.