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Journal of Virology, April 2007, p. 3778-3785, Vol. 81, No. 8
0022-538X/07/$08.00+0     doi:10.1128/JVI.02664-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Minor Capsid Proteins of Simian Virus 40 Are Dispensable for Nucleocapsid Assembly and Cell Entry but Are Required for Nuclear Entry of the Viral Genome{triangledown}

Akira Nakanishi,1,2,{dagger} Noriko Itoh,1 Peggy P. Li,1 Hiroshi Handa,2 Robert C. Liddington,3 and Harumi Kasamatsu1*

Molecular Biology Institute and Department of Molecular, Cell, and Developmental Biology, University of California at Los Angeles, Los Angeles, California 90095,1 Faculty of Bioscience and Biotechnology, Tokyo Institute of Technology and Frontier Collaborative Research Center, Yokohama, 226-8503, Japan,2 Infectious and Inflammatory Disease Center, Burnham Institute for Medical Research, 10901 North Torrey Pines Road, La Jolla, California 920373

Received 2 December 2006/ Accepted 20 January 2007

We investigated the roles of simian virus 40 capsid proteins in the viral life cycle by analyzing point mutants in Vp1 and Vp2/3, as well as a deletion mutant lacking the Vp2/3 coding sequence. The Vp1 mutants (V243E and L245E) and the Vp2/3 mutants (F157E-I158E and P164R-G165E-G166R) were previously shown to be defective in Vp1-Vp2/3 interaction and to be noninfectious or poorly infectious, respectively. Here, we show that all these point mutants form stable particles following DNA transfection into cells. The Vp2/3-mutant particles contained very low levels of Vp2/3, whereas the Vp1 mutant particles contained no detectable Vp2/3. As expected, the deletion mutant also formed particles that were noninfectious. We further characterized the two Vp1 point mutants and the deletion mutant. All three mutant particles comprised Vp1 and histone-associated viral DNA, and all were able to enter cells. However, the mutant complexes failed to associate with host importins (owing to the loss of the Vp2/3 nuclear localization signal), and the mutant viral DNAs prematurely dissociated from the Vp1s, suggesting that the nucleocapsids did not enter the nucleus. Consistently, all three mutant particles failed to express large T antigen. Together, our results demonstrate unequivocally that Vp2/3 is dispensable for the formation of nucleocapsids. Further, the nucleocapsids' ability to enter cells implies that Vp1 contains the major determinants for cell attachment and entry. We propose that the major role of Vp2/3 in infectivity is to mediate the nuclear entry of viral DNA.

* Corresponding author. Mailing address: Molecular Biology Institute, 456 Boyer Hall, University of California, Los Angeles, 611 East Charles E. Young Dr., Box 951570, Los Angeles, CA 90095-1570. Phone: (310) 825-3048. Fax: (310) 206-7286. E-mail: harumi_K{at}mbi.ucla.edu

{triangledown} Published ahead of print on 31 January 2007.

{dagger} Present address: National Institute for Longevity Sciences, National Center for Geriatrics and Gerontology, Obu, Aichi, 474-8522, Japan.

Journal of Virology, April 2007, p. 3778-3785, Vol. 81, No. 8
0022-538X/07/$08.00+0     doi:10.1128/JVI.02664-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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