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J. Virol., 02 1997, 941-948, Vol 71, No. 2
X Xiao, W Xiao, J Li and RJ Samulski
Adeno-associated virus (AAV) replication is dependent on two copies of a
145-bp inverted terminal repeat (ITR) that flank the AAV genome. This is
the primary cis-acting element required for productive infection and the
generation of recombinant AAV (rAAV) vectors. We have engineered a plasmid
(pDD-2) containing only 165 bp of AAV sequence: two copies of the D
element, a unique sequence adjacent to the AAV nicking site, flanking a
single ITR. When assayed in vivo, this modified hairpin was sufficient for
the replication of the plasmid vector when Rep and adenovirus (Ad) helper
functions were supplied in trans. pDD-2 replication intermediates were
characteristic of the AAV replication scheme in which linear monomer,
dimer, and other higher-molecular- weight replicative intermediates are
generated. Compared to infectious AAV clones for replication, the modified
hairpin vector replicated more efficiently independent of size. Further
analysis demonstrated conversion of the input circular plasmid to a linear
substrate with AAV terminal repeat elements at either end as an initial
step for replication. This conversion was independent of both Rep and Ad
helper genes, suggesting the role of host factors in the production of
these molecules. The generation of these substrates suggested resolution of
the modified terminal repeat through a Holliday-like structure rather than
replication as a mechanism for rescue. Production of replicative
intermediates via this plasmid substrate were competent not only for AAV
DNA replication but also for encapsidation, infection, integration, and
subsequent rescue from the chromosome when superinfected with Ad and
wild-type AAV. These studies demonstrate that this novel 165-bp ITR
substrate is sufficient in cis for the AAV life cycle and should provide a
valuable reagent for further dissecting the cis sequences involved in AAV
replication, packaging, and integration. In addition, this novel plasmid
vector can be used as a substrate for both rAAV vector production and
synthetic plasmid vector delivery.
Copyright © 1997, American Society for Microbiology
A novel 165-base-pair terminal repeat sequence is the sole cis requirement for the adeno-associated virus life cycle
Gene Therapy Center and Department of Pharmacology, University of North Carolina at Chapel Hill, 27599, USA.
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