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Journal of Virology, September 2009, p. 8439-8450, Vol. 83, No. 17
0022-538X/09/$08.00+0     doi:10.1128/JVI.00877-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Vaccinia Virus H7 Protein Contributes to the Formation of Crescent Membrane Precursors of Immature Virions {triangledown}

P. S. Satheshkumar, Andrea Weisberg, and Bernard Moss*

Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892-3210

Received 30 April 2009/ Accepted 17 June 2009

Crescent membranes are the first viral structures that can be discerned during poxvirus morphogenesis. The crescents consist of a lipoprotein membrane and an outer lattice scaffold, which provides uniform curvature. Relatively little is known regarding the composition of the crescent membrane or its mode of formation. Here, we show that the H7 protein, which is conserved in all vertebrate poxviruses but has no discernible functional motifs or nonpoxvirus homologs, contributes to the formation of crescents and immature virions. Synthesis of the 17-kDa H7 protein was dependent on DNA replication and occurred late during vaccinia virus infection. Unlike many late proteins, however, H7 was not incorporated into mature virions or localized in cellular organelles. To gain insight into the role of H7, an inducible mutant was constructed and shown to have a conditional lethal phenotype: H7 expression and infectious virus formation were dependent on isopropyl-beta-D-thiogalactopyranoside. In the absence of inducer, viral late proteins were made, but membrane and core proteins were not processed by the I7 protease. A block in morphogenesis was demonstrated by transmission electron microscopy: neither typical crescents nor immature virions were detected in the absence of inducer. Instead, factory areas of the cytoplasm contained large, electron-dense inclusions, some of which had partially coated membrane segments at their surfaces. Separate, lower-density inclusions containing the D13 scaffold protein and endoplasmic reticulum membranes were also present. These features are most similar to those previously seen when expression of A11, another conserved nonvirion protein, is repressed.

* Corresponding author. Mailing address: Laboratory of Viral Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 33 North Drive, MSC 3210, Bethesda, MD 20892-3210. Phone: (301) 496-9869. Fax: (301) 480-1535. E-mail: bmoss{at}nih.gov

{triangledown} Published ahead of print on 24 June 2009.

Journal of Virology, September 2009, p. 8439-8450, Vol. 83, No. 17
0022-538X/09/$08.00+0     doi:10.1128/JVI.00877-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Satheshkumar, P. S., Moss, B. (2009). Characterization of a Newly Identified 35-Amino-Acid Component of the Vaccinia Virus Entry/Fusion Complex Conserved in All Chordopoxviruses. J. Virol. 83: 12822-12832 [Abstract] [Full Text]  


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