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Journal of Virology, June 1999, p. 4728-4737, Vol. 73, No. 6
Laboratory of Molecular Microbiology,
National Institute of Allergy and Infectious Diseases, National
Institutes of Health, Bethesda, Maryland 20892-0460
Received 29 December 1998/Accepted 12 March 1999
We previously characterized mutations in the human immunodeficiency
virus type 1 matrix (MA) protein that displayed reduced infectivity in
single-round assays, defects in the stable synthesis of viral DNA in
infected cells, and impaired endogenous reverse transcriptase activity.
The mutants, which contained substitutions in a highly conserved Leu at
MA amino acid 20, also increased binding of Gag to membrane. To
elucidate further the role of MA in the virus replication cycle, we
have characterized a viral revertant of an amino acid 20 mutant (20LK).
The revertant virus, which replicates with essentially wild-type
kinetics in H9 cells, contains second-site compensatory changes at MA
amino acids 73 (E
0022-538X/99/$04.00+0
Reversion of a Human Immunodeficiency Virus Type 1 Matrix Mutation Affecting Gag Membrane Binding, Endogenous Reverse
Transcriptase Activity, and Virus Infectivity

K) and 82 (A
T), while retaining the original
20LK mutation. Single-cycle infectivity assays, performed with
luciferase-expressing viruses, show that the 20LK/73EK/82AT triple
mutant displays markedly improved infectivity relative to the original
20LK mutant. The stable synthesis of viral DNA in infected cells is
also significantly increased compared with that of 20LK DNA.
Furthermore, activity of revertant virions in endogenous reverse
transcriptase assays is restored to near-wild-type-levels.
Interestingly, although 20LK/73EK/82AT reverses the defects in
replication kinetics, postentry events, and endogenous reverse
transcriptase activity induced by the 20LK mutation, the reversion does
not affect the 20LK-imposed increase in Gag membrane binding. Mutants
containing single and double amino acid substitutions were constructed,
and their growth kinetics were examined. Only virus containing all
three changes (20LK/73EK/82AT) grew with significantly accelerated
kinetics; 73EK, 73EK/82AT, and 20LK/82AT mutants displayed pronounced
defects in virus particle production. Viral core-like complexes were
isolated by sucrose density gradient centrifugation of
detergent-treated virions. Intriguingly, the protein composition of
wild-type and mutant detergent-resistant complexes differed markedly.
In wild-type and 20LK complexes, MA was removed following detergent
solubilization of the viral membrane. In contrast, in revertant
preparations, the majority of MA cosedimented with the
detergent-resistant complex. These results suggest that the
20LK/73EK/82AT mutations induced a significant alteration in MA-MA or
MA-core interactions.
*
Corresponding author. Mailing address: Bldg. 4, Rm.
307, NIAID, NIH, Bethesda, MD 20892-0460. Phone: (301) 402-3215. Fax: (301) 402-0226. E-mail: EFreed{at}nih.gov.
Present address: IGH, CNRS-UPR 1142, Montpellier, France.
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