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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. Kuhn^1,*

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.

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^* 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.

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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.

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