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Journal of Virology, June 2007, p. 6471-6481, Vol. 81, No. 12
0022-538X/07/$08.00+0 doi:10.1128/JVI.02120-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Christopher T. Jones,
,
Yu-hsuan Chang,
Ranjit Warrier, and
Richard J. Kuhn*
Department of Biological Sciences, Purdue University, 915 W. State Street, West Lafayette, Indiana 47907-2054
Received 27 September 2006/ Accepted 23 March 2007
Although it is known that the flavivirus capsid protein is essential for genome packaging and formation of infectious particles, the minimal requirements of the dimeric capsid protein for virus assembly/disassembly have not been characterized. By use of a trans-packaging system that involved packaging a yellow fever virus (YFV) replicon into pseudo-infectious particles by supplying the YFV structural proteins using a Sindbis virus helper construct, the functional elements within the YFV capsid protein (YFC) were characterized. Various N- and C-terminal truncations, internal deletions, and point mutations of YFC were analyzed for their ability to package the YFV replicon. Consistent with previous reports on the tick-borne encephalitis virus capsid protein, YFC demonstrates remarkable functional flexibility. Nearly 40 residues of YFC could be removed from the N terminus while the ability to package replicon RNA was retained. Additionally, YFC containing a deletion of approximately 27 residues of the C terminus, including a complete deletion of C-terminal helix 4, was functional. Internal deletions encompassing the internal hydrophobic sequence in YFC were, in general, tolerated to a lesser extent. Site-directed mutagenesis of helix 4 residues predicted to be involved in intermonomeric interactions were also analyzed, and although single mutations did not affect packaging, a YFC with the double mutation of leucine 81 and valine 88 was nonfunctional. The effects of mutations in YFC on the viability of YFV infection were also analyzed, and these results were similar to those obtained using the replicon packaging system, thus underscoring the flexibility of YFC with respect to the requirements for its functioning.
Published ahead of print on 4 April 2007.
These authors contributed equally to the study.
Present address: Laboratory of Virology and Infectious Disease, The Rockefeller University, 1230 York Avenue, New York, NY 10021.
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