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Journal of Virology, February 2009, p. 1368-1378, Vol. 83, No. 3
0022-538X/09/$08.00+0     doi:10.1128/JVI.01263-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Pre-P Is a Secreted Glycoprotein Encoded as an N-Terminal Extension of the Duck Hepatitis B Virus Polymerase Gene {triangledown}

Feng Cao,1 Catherine A. Scougall,3,4 Allison R. Jilbert,3,4 and John E. Tavis1,2*

Department of Molecular Microbiology and Immunology, Saint Louis University School of Medicine, St. Louis, Missouri,1 Saint Louis University Liver Center, Saint Louis University School of Medicine, St. Louis, Missouri,2 Hepatitis Virus Research, Infectious Diseases Laboratories, Institute of Medical and Veterinary Science, University of Adelaide, Adelaide, SA 5000 Australia,3 School of Molecular and Biomedical Science, University of Adelaide, Adelaide, SA 5005 Australia4

Received 18 June 2008/ Accepted 4 November 2008

The duck hepatitis B virus (DHBV) pregenomic RNA is a bicistronic mRNA encoding the core and polymerase proteins. Thirteen AUGs (C2 to C14) and 10 stop codons (S1 to S10) are located between the C1 AUG for the core protein and the P1 AUG that initiates polymerase translation. We previously found that the translation of the DHBV polymerase is initiated by ribosomal shunting. Here, we assessed the biosynthetic events after shunting. Translation of the polymerase open reading frame was found to initiate at the C13, C14, and P1 AUGs. Initiation at the C13 AUG occurred through ribosomal shunting because translation from this codon was cap dependent but was insensitive to blocking ribosomal scanning internally in the message. C13 and C14 are in frame with P1, and translation from these upstream start codons led to the production of larger isoforms of P. We named these isoforms "pre-P" by analogy to the pre-C and pre-S regions of the core and surface antigen open reading frames. Pre-P was produced in DHBV16 and AusDHBV-infected duck liver and was predicted to exist in 80% of avian hepadnavirus strains. Pre-P was not encapsidated into DHBV core particles, and the viable strain DHBV3 cannot make pre-P, so it is not essential for viral replication. Surprisingly, we found that pre-P is an N-linked glycoprotein that is secreted into the medium of cultured cells. These data indicate that DHBV produces an additional protein that has not been previously reported. Identifying the role of pre-P may improve our understanding of the biology of DHBV infection.

* Corresponding author. Mailing address: Department of Molecular Microbiology and Immunology, Saint Louis University School of Medicine, 1100 S. Grand Blvd., St. Louis, MO 63104. Phone: (314) 977-8893. Fax: (314) 977-8717. E-mail: tavisje{at}slu.edu

{triangledown} Published ahead of print on 12 November 2008.

Journal of Virology, February 2009, p. 1368-1378, Vol. 83, No. 3
0022-538X/09/$08.00+0     doi:10.1128/JVI.01263-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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