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J Virol, June 1998, p. 4678-4685, Vol. 72, No. 6
Departments of Laboratory
Medicine1 and
Internal
Medicine,2 University of California, San
Francisco, California 94143-0100
Received 22 December 1997/Accepted 1 March 1998
The core domain of human immunodeficiency virus type 1 (HIV-1)
integrase (IN) contains a D,D(35)E motif, named for the
phylogenetically conserved glutamic acid and aspartic acid residues and
the invariant 35 amino acid spacing between the second and third acidic
residues. Each acidic residue of the D,D(35)E motif is independently
essential for the 3'-processing and strand transfer activities of
purified HIV-1 IN protein. Using a replication-defective viral genome
with a hygromycin selectable marker, we recently reported that a
mutation at any of the three residues of the D,D(35)E motif produces a 103- to 104-fold reduction in infectious titer
compared with virus encoding wild-type IN (A. D. Leavitt et al.,
J. Virol. 70:721-728. 1996). The infectious titer, as measured by
the number of hygromycin-resistant colonies formed following infection
of cells in culture, was less than a few hundred colonies per µg of
p24. To understand the mechanism by which the mutant virions conferred
hygromycin resistance, we characterized the integrated viral DNA in
cells infected with virus encoding mutations at each of the three
residues of the D,D(35)E motif. We found the integrated viral DNA to be
colinear with the incoming viral genome. DNA sequencing of the
junctions between integrated viral DNA and host DNA showed that (i) the characteristic 5-bp direct repeat of host DNA flanking the HIV-1 provirus was not maintained, (ii) integration often produced a deletion
of host DNA, (iii) integration sometimes occurred without the viral DNA
first undergoing 3'-processing, (iv) integration sites showed a strong
bias for a G residue immediately adjacent to the conserved viral CA
dinucleotide, and (v) mutations at each of the residues of the D,D(35)E
motif produced essentially identical phenotypes. We conclude that
mutations at any of the three acidic residues of the conserved D,D(35)E
motif so severely impair IN activity that most, if not all, integration
events by virus encoding such mutations are not IN mediated.
IN-independent provirus formation may have implications for anti-IN
therapeutic agents that target the IN active site.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Mutations in the Human Immunodeficiency Virus Type
1 Integrase D,D(35)E Motif Do Not Eliminate Provirus
Formation
*
Corresponding author. Mailing address: Department of
Laboratory Medicine, University of California, San Francisco, 505 Parnassus Ave., Room M524D, Box 0100, San Francisco, CA 94143-0100. Phone: (415) 502-8090. Fax: (415) 476-3303. E-mail:
leavitt{at}pangloss.ucsf.edu.
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