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Journal of Virology, February 2001, p. 1359-1370, Vol. 75, No. 3
Departments of Molecular Biology and
Microbiology1 and
Biochemistry,2 Tufts University
School of Medicine, Boston, Massachusetts 02111
Received 31 July 2000/Accepted 18 October 2000
Integration of retrovirus DNA is a specific process catalyzed by
the integrase protein acting to join the viral substrate DNA (att)
sequences of about 10 bases at the ends of the long terminal repeat
(LTR) to various sites in the host target cell DNA. Although the
interaction is sequence specific, the att sequences of different
retroviruses are largely unrelated to one another and usually differ
between the two ends of the viral DNA. To define substrate sequence
specificity, we designed an "in vitro evolution" scheme to select
an optimal substrate sequence by competitive integration in vitro from
a large pool of partially randomized substrates. Integrated substrates
are enriched by PCR amplification and then regenerated and subjected to
subsequent cycles of selection and enrichment. Using this approach, we
obtained the optimal substrate sequence of 5'-ACGACAACA-3'
for avian sarcoma-leukosis virus (ASLV) and
5'-AACA(A/C)AGCA-3' for human immunodeficiency virus type 1, which differed from those found at both ends of the viral DNA. Clonal
analysis of the integration products showed that ASLV integrase can use
a wide variety of substrate sequences in vitro, although the consensus
sequence was identical to the selected sequence. By a competition
assay, the selected nucleotide at position 4 improved the in vitro
integration efficiency over that of the wild-type sequence. Viral
mutants bearing the optimal sequence replicated at wild-type levels,
with the exception of some mutations disrupting the U5 RNA secondary
structure important for reverse transcription, which were significantly
impaired. Thus, maximizing the efficiency of integration may not be of
major importance for efficient retrovirus replication.
0022-538X/01/$04.00+0 DOI: 10.1128/JVI.75.3.1359-1370.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Substrate Sequence Selection by Retroviral
Integrase
*
Corresponding author. Mailing address: Department of
Molecular Biology and Microbiology, Tufts University School of
Medicine, 136 Harrison Ave., Boston, MA 02111. Phone: (617) 636 6528. Fax: (617) 636 4086. E-mail:
jcoffin_par{at}opal.tufts.edu.
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