Journal of Virology, October 1999, p. 7923-7932, Vol. 73, No. 10
Department of Genetics and Developmental
Biology,1 Mary Babb Randolph Cancer
Center,2 and Department of
Biochemistry,3 West Virginia University,
Morgantown, West Virginia 26506
Received 11 March 1999/Accepted 17 June 1999
Deletion of direct repeats in retroviral genomes provides an in
vivo system for analysis of reverse transcriptase (RT) template switching. The effect of distance between direct repeats on the rate of
deletion was determined for 16 murine leukemia virus (MLV)-based vectors containing a 701-bp direct repeat of overlapping fragments of
the herpes simplex virus thymidine kinase gene (HTK). The direct repeats were separated by spacer fragments of various lengths (0.1 to
3.5 kb). Southern analysis of infected cells after one replication
cycle indicated that all vectors in which the distance between
homologous sequences was >1,500 bp deleted at very high rates
(>90%). In contrast, vectors containing <1,500 bp between homologous
sequences exhibited lower frequencies of deletion (37 to 82%). To
analyze the pattern of locations at which RT switched templates,
restriction site markers were introduced to divide the downstream
direct repeat into five regions. RT switched templates within all five
regions of the 701-bp direct repeat and the frequency of template
switching was greater within the 5' regions in comparison to the 3'
regions. The probability of RT switching templates within the 5'
regions doubled when the MLV packaging sequence (
0022-538X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Effect of Distance between Homologous Sequences and
3' Homology on the Frequency of Retroviral Reverse Transcriptase
Template Switching
) was placed
between the 701-bp direct repeats. However,
did not increase the
rate of template switching for shorter direct repeats. These results
indicate that linear distance between homologous sequences increases
the rate of template switching and suggest that duplex formation
between nascent DNA and homologous template sequences 3' of RT promote
template switching.
*
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}WVU.edu.
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