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Journal of Virology, August 2001, p. 7683-7691, Vol. 75, No. 16
The Wistar Institute, Philadelphia,
Pennsylvania 19104
Received 13 February 2001/Accepted 9 May 2001
The RNA genome of human immunodeficiency virus type 1 (HIV-1) is
converted into DNA after infection in order to integrate into the host
cell DNA. However, a large number of these reverse-transcribed genomes
remain unintegrated in the nucleus of infected cells. Currently, there
are no data available about the intranuclear distribution pattern of
unintegrated HIV-1 DNA in relation to nuclear structures as observed on
the single-cell level. In the present study, we investigated the
intranuclear fate of unintegrated viral DNA in cell lines expressing
CD4 and coreceptors (HOS-CD4.CCR5 and U373-MAGI-CXCR4CEM)
infected with HIV-1 (strain 89.6). We used a novel approach to
distinguish in situ unintegrated from integrated viral DNA by
performing fluorescent in situ hybridization on cells in which
stress-induced chromosome condensation had been induced, a procedure
that contracts chromosomes independent of the cell cycle. Cells
infected for 15 h accumulated large amounts of HIV-1 DNA which was
located between the condensed chromosome strands, allowing the
identification of this viral DNA as unintegrated. In contrast,
in HeLa/LAV, a cell line carrying integrated HIV-1 genomes, the great
majority of viral DNA colocalized with the cellular DNA. We show that
unintegrated HIV-1 DNA does not evenly distribute within the host cell
nucleus but tends to aggregate into clusters containing many copies of
the viral genomes. The formation of these DNA clusters was independent
of viral DNA replication and thus appeared to result solely from
multiple infections. The DNA aggregates remained in the nuclei of
infected cells for at least 25 h after the infection was stopped.
The emergence of transcription sites, which most likely denote sites of
the integrated provirus, lagged clearly behind the accumulation of
viral DNA. These transcription foci could not be linked to unintegrated
DNA molecules, suggesting that this DNA type is unable to transcribe,
at least at levels comparable to those of integrated DNA. Neither
unintegrated HIV-1 DNA nor transcription foci nor integrated DNA was
observed to associate with nuclear domain 10 (ND10), a nuclear
structure known to represent the site where several DNA viruses
replicate and transcribe. Also, HIV-1 does not modify ND10 at early or
late times of infection. There was no specific association of HIV-1 transcripts with splicing factor SC35 domains, in contrast to what has
been reported for a number of both cellular and viral genes.
Surprisingly, unintegrated HIV-1 DNA was found to accumulate within or
in close association with SC35 domains, demonstrating a specific
distribution of the viral DNA within the host cell nucleus. Taken
together, our results demonstrate that unintegrated proviral HIV-1 DNA
does not randomly localize within infected cells but preferentially
aggregates in the nucleus within SC35 domains.
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.16.7683-7691.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Accumulation and Intranuclear Distribution of
Unintegrated Human Immunodeficiency Virus Type 1 DNA
*
Corresponding author. Mailing address: The Wistar
Institute, 3601 Spruce St., Philadelphia, PA 19104. Phone: (215)
898-3817. Fax: (215) 898-3868. E-mail:
maul{at}wistar.upenn.edu.
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