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J Virol, July 1998, p. 5789-5796, Vol. 72, No. 7
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

The Duck Hepatitis B Virus Polymerase Is Activated by Its RNA Packaging Signal, epsilon

John E. Tavis,* Brandon Massey, and Yunhao Gong

Department of Molecular Microbiology and Immunology, St. Louis University School of Medicine, St. Louis, Missouri 63104

Received 26 February 1998/Accepted 13 April 1998

The varepsilon  stem-loop at the 5' end of the pregenomic RNA of the hepatitis B viruses is both the primary element of the RNA packaging signal and the origin of reverse transcription. We have previously presented evidence for a third essential role for varepsilon , that of an essential cofactor in the maturation of the viral polymerase (J. E. Tavis and D. Ganem, J. Virol. 70:5741-5750, 1996). In this case, binding of varepsilon  to the polymerase is proposed to induce a physical alteration to the polymerase that is needed for it to develop enzymatic activity. Three lines of evidence employing duck hepatitis B virus supporting this hypothesis are presented here. First, an unusual DNA polymerase activity employing exogenous RNAs (the trans reaction) that was originally discovered with recombinant duck hepatitis B virus polymerase expressed in Saccharomyces cerevisiae yeasts was shown to be an authentic property of the viral polymerase. The trans reaction was found to be template-dependent reverse transcription of the exogenous RNA. The trans reaction occurred independently of the hepadnavirus protein-priming mechanism, yet it was still strongly stimulated by varepsilon . This directly demonstrates a role for varepsilon  in activation of the polymerase. Second, the reverse transcriptase domain of the polymerase was shown to be physically altered following binding to varepsilon , as would be expected if the alteration was required for maturation of the polymerase to an enzymatically active form. Finally, analysis of 15 mutations throughout the duck hepatitis B virus polymerase demonstrated that the varepsilon -dependent alteration to the polymerase was a prerequisite for DNA priming, reverse transcription, and the trans reaction.

* Corresponding author. Mailing address: Department of Molecular Microbiology and Immunology, St. Louis University School of Medicine, 1402 S. Grand Blvd., St. Louis, MO 63104. Phone: (314) 577-8441. Fax: (314) 773-3403. E-mail: tavisje{at}wpogate.slu.edu.

J Virol, July 1998, p. 5789-5796, Vol. 72, No. 7
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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