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J Virol, February 1998, p. 1418-1423, Vol. 72, No. 2
Division of Biology, California Institute of
Technology, Pasadena, California 91125
Received 11 August 1997/Accepted 4 November 1997
Glycoprotein PE2 of Sindbis virus will form a heterodimer with
glycoprotein E1 of Ross River virus that is cleaved to an E2/E1 heterodimer and transported to the cell plasma membrane, but this chimeric heterodimer fails to interact with Sindbis virus
nucleocapsids, and very little budding to produce mature virus occurs
upon infection with chimeric viruses. We have isolated in both Sindbis
virus E2 and in Ross River virus E1 a series of suppressing mutations that adapt these two proteins to one another and allow increased levels
of chimeric virus production. Two adaptive E1 changes in an ectodomain
immediately adjacent to the membrane anchor and five adaptive E2
changes in a 12-residue ectodomain centered on Asp-242 have been
identified. One change in Ross River virus E1 (Gln-411
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Molecular Genetic Study of the Interaction of
Sindbis Virus E2 with Ross River Virus E1 for Virus Budding

Leu) and one
change in Sindbis virus E2 (Asp-248
Tyr) were investigated in detail.
Each change individually leads to about a 10-fold increase in virus
production, and combined the two changes lead to a 100-fold increase in
virus. During passage of a chimeric virus containing Ross River virus
E1 and Sindbis virus E2, the E2 change was first selected, followed by
the E1 change. Heterodimers containing these two adaptive mutations
have a demonstrably increased degree of interaction with Sindbis virus nucleocapsids. In the parental chimera, no interaction between heterodimers and capsids was visible at the plasma membrane in electron
microscopic studies, whereas alignment of nucleocapsids along the
plasma membrane, indicating interaction of heterodimers with
nucleocapsids, was readily seen in the adapted chimera. The significance of these findings in light of our current understanding of
alphavirus budding is discussed.
*
Corresponding author. Mailing address: Division of
Biology 156-29, California Institute of Technology, Pasadena, CA 91125. Phone: (626) 395-4903. Fax: (626) 449-0756. E-mail:
straussj{at}cco.caltech.edu.
Present address: B.C. Research Institute for Child and Family
Health, Vancouver, B.C. V5Z 4H4, Canada.
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