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J Virol, June 1998, p. 5198-5206, Vol. 72, No. 6
Department of Genetics and Developmental
Biology,1
Mary Babb Randolph Cancer
Center,2
Department of Microbiology and
Immunology,3 and
Department of
Biochemistry,4 West Virginia University,
Morgantown, West Virginia 26506
Received 3 November 1997/Accepted 11 February 1998
Retroviral reverse transcriptases (RTs) frequently switch templates
during DNA synthesis, which can result in mutations and recombination.
The relative rates of in vivo RT template switching during RNA- and
DNA-dependent DNA synthesis are unknown. To determine the relative
rates of RT template switching during copying of RNA and DNA templates,
we constructed spleen necrosis virus-based retroviral vectors
containing a 400-bp direct repeat. The directly repeated sequences were
upstream of the polypurine tract (PPT) in the RB-LLP vector; the same
direct repeats flanked the PPT and attachment site (att) in
the RB-LPL vector. RT template switching events could occur during
either RNA- or DNA-dependent DNA synthesis and delete one copy of the
direct repeat plus the intervening sequences. RB-LLP vectors that
underwent direct repeat deletions during RNA- and DNA-dependent DNA
synthesis generated viral DNA that could integrate into the host
genome. However, any deletion of the direct repeats in the RB-LPL
vector that occurred during RNA-dependent DNA synthesis resulted in
deletion of the essential PPT and att site and generated a
dead-end viral DNA product. Thus, only RB-LPL vectors that underwent
direct repeat deletions during DNA-dependent DNA synthesis could
integrate to form proviruses. The RB-LLP and RB-LPL vectors were
permitted to undergo a single replication cycle, and the frequencies of
direct repeat deletions were determined by PCR and Southern analysis of
the resulting proviruses. A comparison of the frequency of direct
repeat deletions in the RB-LLP and RB-LPL vectors indicated that the in
vivo rates of RT template switching during RNA- and DNA-dependent DNA
synthesis are nearly identical.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Relative Rates of Retroviral Reverse Transcriptase
Template Switching during RNA- and DNA-Dependent DNA
Synthesis
*
Corresponding author. Mailing address: Mary Babb
Randolph Cancer Center, West Virginia University, Morgantown, WV 26506. Phone: (304) 293-0495. Fax: (304) 293-4667. E-mail:
VPATHAK{at}WVUMBRCC1.hsc.wvu.edu.
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