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Journal of Virology, June 2000, p. 5142-5150, Vol. 74, No. 11
Laboratory of Molecular Microbiology,
National Institute of Allergy and Infectious Diseases, National
Institutes of Health, Bethesda, Maryland 20892-0460
Received 23 December 1999/Accepted 10 March 2000
The human immunodeficiency virus type 1 (HIV-1) Gag precursor,
Pr55Gag, is necessary and sufficient for the assembly and
release of viruslike particles. Binding of Gag to membrane and Gag
multimerization are both essential steps in virus assembly, yet the
domains responsible for these events have not been fully defined. In
addition, the relationship between membrane binding and Gag-Gag
interaction remains to be elucidated. To investigate these issues, we
analyzed, in vivo, the membrane-binding and assembly properties of a
series of C-terminally truncated Gag mutants. Pr55Gag was
truncated at the C terminus of matrix (MAstop), between the N- and
C-terminal domains of capsid (CA146stop), at the C terminus of capsid
(p41stop), at the C terminus of p2 (p43stop), and after the N-terminal
35 amino acids of nucleocapsid (NC35stop). The ability of these
truncated Gag molecules to assemble and release viruslike particles and
their capacity to copackage into particles when coexpressed with
full-length Gag were determined. We demonstrate that the amount of
truncated Gag incorporated into particles is incrementally increased by
extension from CA146 to NC35, suggesting that multiple sites in this
region are involved in Gag multimerization. Using membrane flotation
centrifugation, we observe that MA shows significantly reduced membrane
binding relative to full-length Gag but that CA146 displays
steady-state membrane-binding properties comparable to those of
Pr55Gag. The finding that the CA146 mutant, which contains
only matrix and the N-terminal domain of capsid, exhibits levels of
steady-state membrane binding equivalent to those of full-length Gag
indicates that strong Gag-Gag interaction domains are not required for
the efficient binding of HIV-1 Gag to membrane.
0022-538X/00/$04.00+0
Relationship between Human Immunodeficiency Virus
Type 1 Gag Multimerization and Membrane Binding
*
Corresponding author. Mailing address: Bldg. 4, Rm.
307, NIAID, NIH, 9000 Rockville Pike, Bethesda, MD 20892-0460. Phone: (301) 402-3215. Fax: (301) 402-0226. E-mail: EFreed{at}nih.gov.
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