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Journal of Virology, August 2009, p. 8032-8040, Vol. 83, No. 16
0022-538X/09/$08.00+0     doi:10.1128/JVI.00332-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Four Conserved Cysteine Residues of the Hepatitis B Virus Polymerase Are Critical for RNA Pregenome Encapsidation{triangledown}

Seahee Kim, Jehan Lee, and Wang-Shick Ryu*

Department of Biochemistry, Yonsei University, Seoul, Korea 120-749

Received 14 February 2009/ Accepted 3 June 2009

Hepadnaviruses replicate via reverse transcription of an RNA template, the pregenomic RNA (pgRNA). Although hepadnaviral polymerase (Pol) and retroviral reverse transcriptase are distantly related, some of their features are distinct. In particular, Pol contains two additional N-terminal subdomains, the terminal protein and spacer subdomains. Since much of the spacer subdomain can be deleted without detrimental effects to hepatitis B virus (HBV) replication, this subdomain was previously thought to serve only as a spacer that links the terminal protein and reverse transcriptase subdomains. Unexpectedly, we found that the C terminus of the spacer subdomain is indispensable for the encapsidation of pgRNA. Alanine-scanning mutagenesis revealed that four conserved cysteine residues, three at the C terminus of the spacer subdomain and one at the N terminus of the reverse transcriptase subdomain, are critical for encapsidation. The inability of the mutant Pol proteins to incorporate into nucleocapsid particles, together with other evidence, argued that the four conserved cysteine residues are critical for RNA binding. One implication is that these four cysteine residues might form a putative zinc finger motif. Based on these findings, we speculate that the RNA binding activity of HBV Pol may be mediated by this newly identified putative zinc finger motif.

* Corresponding author. Mailing address: 134 Shinchondong, Seodaemungu, Seoul, Korea 120-749. Phone: 82-2-2123-2708. Fax: 82-2-362-9897. E-mail: wsryu{at}yonsei.ac.kr

{triangledown} Published ahead of print on 10 June 2009.

Journal of Virology, August 2009, p. 8032-8040, Vol. 83, No. 16
0022-538X/09/$08.00+0     doi:10.1128/JVI.00332-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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