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Journal of Virology, January 2001, p. 1-10, Vol. 75, No. 1
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.1.1-10.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Alphavirus Nucleocapsid Protein Contains a Putative
Coiled Coil
-Helix Important for Core Assembly
Rushika
Perera,1
Katherine E.
Owen,1,
Timothy L.
Tellinghuisen,1
Alexander E.
Gorbalenya,2 and
Richard J.
Kuhn1,*
Department of Biological Sciences, Purdue
University, West Lafayette, Indiana 47907,1 and
Advanced Biomedical Computing Center, SAIC/NCI, Frederick
Cancer Research and Development Center, Frederick, Maryland
217022
Received 28 July 2000/Accepted 3 October 2000
The alphavirus nucleocapsid core is formed through the energetic
contributions of multiple noncovalent interactions mediated by the
capsid protein. This protein consists of a poorly conserved N-terminal
region of unknown function and a C-terminal conserved autoprotease
domain with a major role in virion formation. In this study, an
18-amino-acid conserved region, predicted to fold into an
-helix
(helix I) and embedded in a low-complexity sequence enriched with basic
and Pro residues, has been identified in the N-terminal region of the
alphavirus capsid proteins. In Sindbis virus, helix I spans residues 38 to 55 and contains three conserved leucine residues, L38, L45, and L52,
conforming to the heptad amino acid organization evident in leucine
zipper proteins. Helix I consists of an N-terminally truncated heptad
and two complete heptad repeats with
-branched residues and
conserved leucine residues occupying the a and
d positions of the helix, respectively. Complete or partial
deletion of helix I, or single-site substitutions at the conserved
leucine residues (L45 and L52), caused a significant decrease in virus
replication. The mutant viruses were more sensitive to elevated
temperature than wild-type virus. These mutant viruses also failed to
accumulate cores in the cytoplasm of infected cells, although they did
not have defects in protein translation or processing. Analysis of
these mutants using an in vitro assembly system indicated that the
majority were defective in core particle assembly. Furthermore, mutant
proteins showed a trans-dominant negative phenotype in in
vitro assembly reactions involving mutant and wild-type proteins. We
propose that helix I plays a central role in the assembly of nucleocapsid cores through coiled coil interactions. These interactions may stabilize subviral intermediates formed through the interactions of
the C-terminal domain of the capsid protein and the genomic RNA and
contribute to the stability of the virion.
*
Corresponding author. Mailing address: Department of
Biological Sciences, Purdue University, West Lafayette, IN 47907. Phone: (765) 494-1164. Fax: (765) 496-1189. E-mail:
rjkuhn{at}bragg.bio.purdue.edu.

Present address: Merck Research Laboratories, Merck and Co.,
West Point, PA
19486.
Journal of Virology, January 2001, p. 1-10, Vol. 75, No. 1
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.1.1-10.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
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