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Journal of Virology, September 2007, p. 10137-10150, Vol. 81, No. 18
0022-538X/07/$08.00+0     doi:10.1128/JVI.01233-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Murine Gammaherpesvirus 68 ORF52 Encodes a Tegument Protein Required for Virion Morphogenesis in the Cytoplasm

Eric Bortz,^1, Lili Wang,⁵ Qingmei Jia,² Ting-Ting Wu,² Julian P. Whitelegge,³ Hongyu Deng,^4,5 Z. Hong Zhou,⁶ and Ren Sun^1,2,4*

Molecular Biology IDP,¹ Department of Molecular and Medical Pharmacology,² the Pasarow Mass Spectrometry Laboratory and NPI-Semel Institute for Neuroscience and Human Behavior, David Geffen School of Medicine,³ School of Dentistry, University of California at Los Angeles, Los Angeles, California 90095,⁴ Center for Infection and Immunity, National Laboratory for Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Beijing, China,⁵ Department of Pathology and Laboratory Medicine, University of Texas—Houston Medical School, Houston, Texas 77030⁶

Received 13 June 2006/ Accepted 26 June 2007

The tegument, a semiordered matrix of proteins overlying the nucleocapsid and underlying the virion envelope, in viruses in the gamma subfamily of Herpesviridae is poorly understood. Murine gammaherpesvirus 68 (MHV-68) is a robust model for studying gammaherpesvirus virion structure, assembly, and composition, as MHV-68 efficiently completes the lytic phase and productively infects cultured cells. We have found that MHV-68 ORF52 encodes an abundant tegument protein conserved among gammaherpesviruses. Detergent sensitivity experiments revealed that the MHV-68 ORF52 protein is more tightly bound to the virion nucleocapsid than the ORF45 tegument protein but could be dissociated from particles that retained the ORF65 small capsomer protein. ORF52, tagged with enhanced green fluorescent protein or FLAG epitope, localized to the cytoplasm. A recombinant MHV-68 bacterial artificial chromosome mutant with a nonsense mutation incorporated into ORF52 exhibited viral DNA replication, expression of late lytic genes, and capsid assembly and packaging at levels near those of the wild type. However, the MHV-68 ORF52-null virus was deficient in the assembly and release of infectious virion particles. Instead, partially tegumented capsids produced by the ORF52-null mutant accumulated in the cytoplasm, containing conserved capsid proteins, the ORF64 and ORF67 tegument proteins, but virtually no ORF45 tegument protein. Thus, ORF52 is essential for the tegumentation and egress of infectious MHV-68 particles in the cytoplasm, suggesting an important conserved function in gammaherpesvirus virion morphogenesis.

Published ahead of print on 18 July 2007.

Present address: Department of Microbiology, Mount Sinai School of Medicine, New York, NY 10021.

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