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J. Biol. Chem., Vol. 282, Issue 16, 12210-12219, April 20, 2007

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A Role for Molecular Chaperone Hsc70 in Reovirus Outer Capsid Disassembly^*

Tijana Ivanovic¹, Melina A. Agosto^¶2, Kartik Chandran³, and Max L. Nibert^¶4

From the Department of Microbiology and Molecular Genetics, Harvard Medical School and Training Programs in Virology and^¶Biological and Biomedical Sciences, Harvard University, Boston, Massachusetts 02115

After crossing the cellular membrane barrier during cell entry, most animal viruses must undergo further disassembly before initiating viral gene expression. In many cases, these disassembly mechanisms remain poorly defined. For this report, we examined a final step in disassembly of the mammalian reovirus outer capsid: cytoplasmic release of the central, fragment of membrane penetration protein µ1 to yield the transcriptionally active viral core particle. An in vitro assay with reticulocyte lysate recapitulated the release of intact molecules. Requirements for activity in this system were shown to include a protein factor, ATP, and Mg²⁺ and K⁺ ions, consistent with involvement of a molecular chaperone such as Hsc70. Immunodepletion of Hsc70 and Hsp70 impaired release, which was then rescued by addition of purified Hsc70. Hsc70 was associated with released molecules not only in the lysate but also during cell entry. We conclude that Hsc70 plays a defined role in reovirus outer capsid disassembly, during or soon after membrane penetration, to prepare the entering particle for gene expression and replication.

Received for publication, November 2, 2006 , and in revised form, January 30, 2007.

^* This work was supported in part by National Institutes of Health Grants F31 AI064142 (to M. A. A.) and R01 AI46440 (to M. L. N.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Supported by National Institutes of Health Grant T32 AI07245 to the training program in Virology.

² Supported by National Institutes of Health Grant T32 GM07226 to the training program in Biological and Biomedical Sciences.

³ Supported by a Bernard N. Fields fellowship to the Department of Microbiology and Molecular Genetics from Ruth Peedin Fields. Present address: Dept. of Microbiology, Albert Einstein College of Medicine, Bronx, NY 10461.

⁴ To whom correspondence should be addressed: Dept. of Microbiology and Molecular Genetics, Harvard Medical School, 200 Longwood Ave., Boston, MA 02115. Tel.: 617-432-4838; Fax: 617-738-7664; E-mail: mnibert{at}hms.harvard.edu.

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