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Journal of Virology, September 2000, p. 8188-8193, Vol. 74, No. 17
Department of Cancer Immunology and AIDS,
Dana-Farber Cancer Institute, and Department of Pathology, Harvard
Medical School, Boston, Massachusetts 02115
Received 27 January 2000/Accepted 7 June 2000
Two activities of retroviral integrase, 3' processing and DNA
strand transfer, are required to integrate viral cDNA into a host cell
chromosome. Integrase activity has been analyzed in vitro using
purified protein and recombinant DNA substrates that model the U3 and
U5 ends of viral cDNA or by using viral preintegration complexes (PICs)
that form during virus infection. Numerous studies have investigated
changes in integrase or viral DNA for effects on both 3' processing and
DNA strand transfer activities using purified protein, but similar
analyses have not been carried out using PICs. Here, we analyzed PICs
from human immunodeficiency virus type 1 (HIV-1) strain 604del, an
integration-defective mutant lacking 26 bp of U5, and revE1, a
revertant of 604del containing an additional 19-bp deletion, for levels
of 3' processing activity that occurred in infected cells and for
levels of in vitro DNA strand transfer activity. Whereas revE1
supported one-third to one-half of the level of wild-type DNA strand
transfer activity, the level of 604del DNA strand transfer activity was
undetectable. Surprisingly, integrase similarly processed the 3' ends
of 604del and revE1 in vivo. We therefore conclude that 604del is
blocked in its ability to replicate in cells after the 3' processing
step of retroviral integration. Whereas Western blotting showed that wild-type, revE1, and 604del PICs contained similar levels of integrase
protein, Mu-mediated PCR footprinting revealed only minimal protein-DNA
complex formation at the ends of 604del cDNA. We propose that 604del is
replication defective because proteins important for DNA strand
transfer activity do not stably associate with this cDNA after in vivo
3' processing by integrase.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Characterization of a Replication-Defective Human
Immunodeficiency Virus Type 1 att Site Mutant That Is
Blocked after the 3' Processing Step of Retroviral
Integration
*
Corresponding author. Mailing address: Department of
Cancer Immunology and AIDS, Dana-Farber Cancer Institute, 44 Binney
St., Boston, MA 02115. Phone: (617) 632-4361. Fax: (617) 632-3113. E-mail: alan_engelman{at}dfci.harvard.edu.
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