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Journal of Virology, April 2003, p. 4471-4480, Vol. 77, No. 8
0022-538X/03/$08.00+0     DOI: 10.1128/JVI.77.8.4471-4480.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Heat Shock Protein 90-Independent Activation of Truncated Hepadnavirus Reverse Transcriptase

Xingtai Wang,1 Xiaofeng Qian,2 Hwai-Chen Guo,2 and Jianming Hu1*

Departments of Microbiology,1 Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts 021182

Received 8 November 2002/ Accepted 14 January 2003

The reverse transcriptase (RT) encoded by hepadnaviruses (hepatitis B viruses) is a multifunctional protein critical for several aspects of viral assembly and replication. Reverse transcription is triggered by the specific interaction between the RT and an RNA signal located on the viral pregenomic RNA, termed {varepsilon}, and is initiated through a novel protein priming mechanism whereby the RT itself serves as a protein primer and {varepsilon} serves as the obligatory template. Using the RT from duck hepatitis B virus as a model, we previously demonstrated that RT-{varepsilon} interaction and protein priming require the assistance of a host cell chaperone complex, heat shock protein 90 (Hsp90) and its cochaperones, which associates with the RT and facilitates the folding of the RT into an active conformation. We now report that extensive truncation removing the entire C-terminal RNase H domain and part of the central RT domain could relieve this dependence on Hsp90 for RT folding such that the truncated RT variants could function in {varepsilon} interaction and protein priming independently of Hsp90. The presence of certain nonionic or zwitterionic detergent was sufficient to establish and maintain the truncated RT proteins in an active, albeit labile, state. Furthermore, we were able to refold an RT truncation variant de novo after complete denaturation. In contrast, the full-length RT and also RT variants with less-extensive C-terminal truncations required Hsp90 for activation. Surprisingly, the presence of detergent plus some yet-to-be-identified cytoplasmic factor(s) led to a dramatic suppression of the RT activities. These results have important implications for RT folding and conformational maturation, Hsp90 chaperone function, and potential inhibition of RT functions by host cell factors.

* Corresponding author. Mailing address: Department of Microbiology, Boston University School of Medicine, 80 E. Concord St., Rm. R516, Boston, MA 02118. Phone: (617) 638-4982. Fax: (617) 638-4286. E-mail: jmhu{at}bu.edu.

Journal of Virology, April 2003, p. 4471-4480, Vol. 77, No. 8
0022-538X/03/$08.00+0     DOI: 10.1128/JVI.77.8.4471-4480.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Lin, L., Wan, F., Hu, J. (2008). Functional and Structural Dynamics of Hepadnavirus Reverse Transcriptase during Protein-Primed Initiation of Reverse Transcription: Effects of Metal Ions. J. Virol. 82: 5703-5714 [Abstract] [Full Text]  
  • Lin, L., Hu, J. (2008). Inhibition of Hepadnavirus Reverse Transcriptase-{varepsilon} RNA Interaction by Porphyrin Compounds. J. Virol. 82: 2305-2312 [Abstract] [Full Text]  
  • Stahl, M., Beck, J., Nassal, M. (2007). Chaperones Activate Hepadnavirus Reverse Transcriptase by Transiently Exposing a C-Proximal Region in the Terminal Protein Domain That Contributes to {varepsilon} RNA Binding. J. Virol. 81: 13354-13364 [Abstract] [Full Text]  
  • Stahl, M., Retzlaff, M., Nassal, M., Beck, J. (2007). Chaperone activation of the hepadnaviral reverse transcriptase for template RNA binding is established by the Hsp70 and stimulated by the Hsp90 system. Nucleic Acids Res 35: 6124-6136 [Abstract] [Full Text]  
  • Keppler, B. R., Grady, A. T., Jarstfer, M. B. (2006). The Biochemical Role of the Heat Shock Protein 90 Chaperone Complex in Establishing Human Telomerase Activity. J. Biol. Chem. 281: 19840-19848 [Abstract] [Full Text]  
  • Hu, J., Boyer, M. (2006). Hepatitis B Virus Reverse Transcriptase and {varepsilon} RNA Sequences Required for Specific Interaction In Vitro. J. Virol. 80: 2141-2150 [Abstract] [Full Text]  
  • Hu, J., Flores, D., Toft, D., Wang, X., Nguyen, D. (2004). Requirement of Heat Shock Protein 90 for Human Hepatitis B Virus Reverse Transcriptase Function. J. Virol. 78: 13122-13131 [Abstract] [Full Text]  


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