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J. Virol., 02 1997, 971-980, Vol 71, No. 2
AQ Baldauf, K Willwand, E Mumtsidu, JP Nuesch and J Rommelaere
We have developed an in vitro system that supports the replication of
natural DNA templates of the autonomous parvovirus minute virus of mice
(MVM). MVM virion DNA, a single-stranded molecule bracketed by short,
terminal, self-complementary sequences, is converted into double- stranded
replicative-form (RF) DNA when incubated in mouse A9 fibroblast extract.
The 3' end of the newly synthesized complementary strand is ligated to the
right-end hairpin of the virion strand, resulting in the formation of a
covalently closed RF (cRF) molecule as the major conversion product. cRF
DNA is not further replicated in A9 cell extract alone. On addition of
purified MVM nonstructural protein NS1 expressed from recombinant
baculoviruses or vaccinia viruses, cRF DNA is processed into a right-end
(5' end of the virion strand) extended form (5'eRF). This is indicative of
NS1-dependent nicking of the right-end hairpin at a distinct position,
followed by unfolding of the hairpin and copying of the terminal sequence.
In contrast, no resolution of the left-end hairpin can be detected in the
presence of NS1. In the course of the right-end nicking reaction, NS1 gets
covalently attached to the right-end telomere of the DNA product, as shown
by immunoprecipitation with NS1-specific antibodies. The 5'eRF product is
the target for additional rounds of NS1-induced nicking and displacement
synthesis at the right end, arguing against the requirement of the hairpin
structure for recognition of the DNA substrate by NS1. Further processing
of the 5'eRF template in vitro leads to the formation of dimeric RF (dRF)
DNA in a left-to-left-end configuration, presumably as a result of copying
of the whole molecule by displacement synthesis initiated at the right-end
telomere. Formation of dRF DNA is highly stimulated by NS1. The
experimental results presented in this report support various assumptions
of current models of parvovirus DNA replication and provide new insights
into the replication functions of the NS1 protein.
Copyright © 1997, American Society for Microbiology
Specific initiation of replication at the right-end telomere of the closed species of minute virus of mice replicative-form DNA
Department of Applied Tumor Virology, Deutches Krebsforschungszentrum, Heidelberg, Germany.
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