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Journal of Virology, August 2000, p. 6725-6733, Vol. 74, No. 15
Research Program in Cellular Biotechnology,
Institute of Biotechnology, FIN-00014 University of
Helsinki,1 and Department of
Biochemistry and Pharmacy, Abo Akademi University, FIN-20521
Turku,2 Finland
Received 21 January 2000/Accepted 26 April 2000
The membrane-associated alphavirus RNA replication complex contains
four virus-encoded subunits, the nonstructural proteins nsP1 to nsP4.
Semliki Forest virus (SFV) nsP1 is hydrophobically modified by
palmitoylation of cysteines 418 to 420. Here we show that Sindbis virus
nsP1 is also palmitoylated on the same site (cysteine 420). When
mutations preventing nsP1 palmitoylation were introduced into the
genomes of these two alphaviruses, the mutant viruses remained viable
and replicated to high titers, although their growth was slightly
delayed. The subcellular distribution of palmitoylation-defective nsP1
was altered in the mutant: it no longer localized to filopodial
extensions, and a fraction of it was soluble. The ultrastructure of the
alphavirus replication sites appeared normal, and the localization of
the other nonstructural proteins was unaltered in the mutants. In both
wild-type- and mutant-virus-infected cells, SFV nsP3 and nsP4 could be
extracted from membranes only by alkaline solutions whereas the
nsP2-membrane association was looser. Thus, the membrane binding
properties of the alphavirus RNA replication complex were not
determined by the palmitoylation of nsP1. The nsP1
palmitoylation-defective alphaviruses produced normal plaques in
several cell types, but failed to give rise to plaques in HeLa cells,
although they induced normal apoptosis of these cells. The SFV mutant
was apathogenic in mice: it caused blood viremia, but no infectious
virus was detected in the brain.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Effects of Palmitoylation of Replicase Protein nsP1
on Alphavirus Infection


*
Corresponding author. Mailing address: Institute of
Biotechnology, P.O. Box 56 (Viikinkaari 9), FIN-00014 University of
Helsinki, Finland. Phone: 358-9-19158902. Fax: 358-9-19158952. E-mail:
Petri.Auvinen{at}Helsinki.Fi.
Present address: Institute for Molecular Virology, University of
Wisconsin, Madison, WI 53706.
Present address: The Burnham Institute, La Jolla, CA 92037.
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