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Journal of Virology, October 1998, p. 7722-7732, Vol. 72, No. 10
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Cytomegalovirus Assembly Protein Precursor and
Proteinase Precursor Contain Two Nuclear Localization Signals That
Mediate Their Own Nuclear Translocation and That of the Major
Capsid Protein
Scott M.
Plafker
and
Wade
Gibson*
Virology Laboratories, Department of
Pharmacology and Molecular Sciences, Baltimore, Maryland 21205
Received 6 March 1998/Accepted 12 June 1998
The cytomegalovirus (CMV) assembly protein precursor (pAP)
interacts with the major capsid protein (MCP), and this interaction is
required for nuclear translocation of the MCP, which otherwise remains
in the cytoplasm of transfected cells (L. J. Wood et al., J. Virol. 71:179-190, 1997). We have interpreted this finding to indicate
that the CMV MCP lacks its own nuclear localization signal (NLS) and
utilizes the pAP as an NLS-bearing escort into the nucleus. The CMV pAP
amino acid sequence has two clusters of basic residues (e.g., KRRRER
[NLS1] and KARKRLK [NLS2], for simian CMV) that resemble the simian
virus 40 large-T-antigen NLS (D. Kalderon et al., Cell 39:499-509,
1984) and one of these (NLS1) has a counterpart in the pAP homologs of
other herpesviruses. The work described here establishes that NLS1 and
NLS2 are mutually independent NLS that can act (i) in cis
to translocate pAP and the related proteinase precursor (pNP1) into the
nucleus and (ii) in trans to transport MCP into the
nucleus. By using combinations of NLS mutants and carboxy-terminal
deletion constructs, we demonstrated a self-interaction of pAP and
cytoplasmic interactions of pAP with pNP1 and of pNP1 with itself. The
relevance of these findings to early steps in capsid assembly, the
mechanism of MCP nuclear transport, and the possible cytoplasmic
formation of protocapsomeric substructures is discussed.
*
Corresponding author. Mailing address: Virology
Laboratories, Department of Pharmacology and Molecular Sciences, Johns
Hopkins University School of Medicine, 725 N. Wolfe St., Baltimore, MD 21205. Phone: (410) 955-8680. Fax: (410) 955-3023. E-mail:
Wade_Gibson{at}qmail.bs.jhu.edu.

Present address: Department of Internal Medicine, University of
Virginia, Charlottesville, Va.
Journal of Virology, October 1998, p. 7722-7732, Vol. 72, No. 10
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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