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Journal of Virology, April 2002, p. 3544-3553, Vol. 76, No. 7
0022-538X/02/$04.00+0 DOI: 10.1128/JVI.76.7.3544-3553.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Dyson Vision Research Institute, Departments of Ophthalmology and Cell Biology, Joan and Sanford Weill Medical College of Cornell University, New York, New York 10021,1 Department of Microbiology, Mount Sinai School of Medicine, New York, New York 100292
Received 16 August 2001/ Accepted 26 December 2001
Influenza virions bud preferentially from the apical plasma membrane of infected epithelial cells, by enveloping viral nucleocapsids located in the cytosol with its viral integral membrane proteins, i.e., hemagglutinin (HA), neuraminidase (NA), and M2 proteins, located at the plasma membrane. Because individually expressed HA, NA, and M2 proteins are targeted to the apical surface of the cell, guided by apical sorting signals in their transmembrane or cytoplasmic domains, it has been proposed that the polarized budding of influenza virions depends on the interaction of nucleocapsids and matrix proteins with the cytoplasmic domains of HA, NA, and/or M2 proteins. Since HA is the major protein component of the viral envelope, its polarized surface delivery may be a major force that drives polarized viral budding. We investigated this hypothesis by infecting MDCK cells with a transfectant influenza virus carrying a mutant form of HA (C560Y) with a basolateral sorting signal in its cytoplasmic domain. C560Y HA was expressed nonpolarly on the surface of infected MDCK cells. Interestingly, viral budding remained apical in C560Y virus-infected cells, and so did the location of NP and M1 proteins at late times of infection. These results are consistent with a model in which apical viral budding is a shared function of various viral components rather than a role of the major viral envelope glycoprotein HA.
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