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Journal of Virology, September 2002, p. 8667-8674, Vol. 76, No. 17
0022-538X/02/$04.00+0     DOI: 10.1128/JVI.76.17.8667-8674.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Cytomegalovirus Assemblin (pUL80a): Cleavage at Internal Site Not Essential for Virus Growth; Proteinase Absent from Virions

Chee-Kai Chan, Edward J. Brignole, and Wade Gibson*

Virology Laboratories, Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205

Received 9 April 2002/ Accepted 3 June 2002

The human cytomegalovirus (HCMV) maturational proteinase is synthesized as an enzymatically active 74-kDa precursor that cleaves itself at four sites. Two of these, called the maturational (M) and release (R) sites, are conserved in the homologs of all herpesviruses. The other two, called the internal (I) and cryptic (C) sites, have recognized consensus sequences only among cytomegalovirus (CMV) homologs and are located in the 28-kDa proteolytic portion of the precursor, called assemblin. I-site cleavage cuts assemblin in half without detected effect on its enzymatic behavior in vitro. To investigate the requirement for this cleavage during virus infection, we used the CMV-bacterial artificial chromosome system (E. M. Borst, G. Hahn, U. H. Koszinowski, and M. Messerle, J. Virol. 73:8320-8329, 1999) to construct a virus encoding a mutant I site (Ala143 to Val) intended to be blocked for cleavage. Characterizations of the resulting mutant (i) confirmed the presence of the mutation in the viral genome and the inability of the mutant virus to effect I-site cleavage in infected cells; (ii) determined that the mutation has no gross effect on the rate of virus production or on the amounts of extracellular virions, noninfectious enveloped particles (NIEPs), and dense bodies; (iii) established that assemblin and its cleavage products are present in NIEPs but are absent from CMV virions, an apparent difference from what is found for virions of herpes simplex virus; and (iv) showed that the 23-kDa protein product of C-site cleavage is more abundant in mutant virus-than in wild-type virus-infected cells and NIEPs. We conclude that the production of infectious CMV requires neither I-site cleavage of assemblin nor the presence of assemblin in the mature virion.

* Corresponding author. Mailing address: Virology Laboratories, Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, 725 N. Wolfe St., Baltimore, MD 21205. Phone: (410) 955-8680. Fax: (410) 955-3023. E-mail: wgibson{at}jhmi.edu.

Journal of Virology, September 2002, p. 8667-8674, Vol. 76, No. 17
0022-538X/02/$04.00+0     DOI: 10.1128/JVI.76.17.8667-8674.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Nguyen, N. L., Loveland, A. N., Gibson, W. (2008). Nuclear Localization Sequences in Cytomegalovirus Capsid Assembly Proteins (UL80 Proteins) Are Required for Virus Production: Inactivating NLS1, NLS2, or Both Affects Replication to Strikingly Different Extents. J. Virol. 82: 5381-5389 [Abstract] [Full Text]  
  • Brignole, E. J., Gibson, W. (2007). Enzymatic Activities of Human Cytomegalovirus Maturational Protease Assemblin and Its Precursor (pPR, pUL80a): Maximal Activity of pPR Requires Self-Interaction through Its Scaffolding Domain. J. Virol. 81: 4091-4103 [Abstract] [Full Text]  
  • Loveland, A. N., Nguyen, N. L., Brignole, E. J., Gibson, W. (2007). The Amino-Conserved Domain of Human Cytomegalovirus UL80a Proteins Is Required for Key Interactions during Early Stages of Capsid Formation and Virus Production. J. Virol. 81: 620-628 [Abstract] [Full Text]  
  • Loveland, A. N., Chan, C.-K., Brignole, E. J., Gibson, W. (2005). Cleavage of Human Cytomegalovirus Protease pUL80a at Internal and Cryptic Sites Is Not Essential but Enhances Infectivity. J. Virol. 79: 12961-12968 [Abstract] [Full Text]  
  • McCartney, S. A., Brignole, E. J., Kolegraff, K. N., Loveland, A. N., Ussin, L. M., Gibson, W. (2005). Chemical Rescue of I-site Cleavage in Living Cells and in Vitro Discriminates between the Cytomegalovirus Protease, Assemblin, and Its Precursor, pUL80a. J. Biol. Chem. 280: 33206-33212 [Abstract] [Full Text]  


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