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Journal of Virology, May 1999, p. 3524-3533, Vol. 73, No. 5
Department of Cell Biology and Anatomy,
University of Alberta, Edmonton, Alberta T6G 2H7, Canada
Received 15 October 1998/Accepted 26 January 1999
Rubella virus is a small enveloped positive-strand RNA virus that
assembles on intracellular membranes in a variety of cell types. The
virus structural proteins contain all of the information necessary to
mediate the assembly of virus-like particles in the Golgi complex. We
have recently identified intracellular retention signals within the two
viral envelope glycoproteins. E2 contains a Golgi retention signal in
its transmembrane domain, whereas a signal for retention in the
endoplasmic reticulum has been localized to the transmembrane and
cytoplasmic domains of E1 (T. C. Hobman, L. Woodward, and M. G. Farquhar, Mol. Biol. Cell 6:7-20, 1995; T. C. Hobman, H. F. Lemon, and K. Jewell, J. Virol. 71:7670-7680, 1997). In the
present study, we have analyzed the role of these retention signals in
the assembly of rubella virus-like particles. Deletion or replacement
of these domains with analogous regions from other type I membrane
glycoproteins resulted in failure of rubella virus-like particles to be
secreted from transfected cells. The E1 transmembrane and cytoplasmic
domains were not required for targeting of the structural proteins to
the Golgi complex and, surprisingly, assembly and budding of virus
particles into the lumen of this organelle; however, the resultant
particles were not secreted. In contrast, replacement or alteration of
the E2 transmembrane or cytoplasmic domain, respectively, abrogated the
targeting of the structural proteins to the budding site, and
consequently, no virion formation was observed. These results indicate
that the transmembrane and cytoplasmic domains of E2 and E1 are
required for early and late steps respectively in the viral assembly
pathway and that rubella virus morphogenesis is very different from
that of the structurally similar alphaviruses.
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Role of Rubella Virus Glycoprotein Domains in
Assembly of Virus-Like Particles
*
Corresponding author. Mailing address: Department of
Cell Biology and Anatomy, University of Alberta, 5-14 Medical Sciences Building, Edmonton, Alberta T6G 2H7, Canada. Phone: (780) 492-6485. Fax: (780) 492-0450. E-mail:
thobman{at}anat.med.ualberta.ca.
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