THE MINUTE VIRUS OF MICE (MVM) NONSTRUCTURAL PROTEIN NS1 INDUCES NICKING OF MVM DNA AT A UNIQUE SITE OF THE RIGHT-END TELOMERE IN BOTH HAIRPIN AND DUPLEX CONFORMATIONS IN-VITRO
K. Willwand et al., THE MINUTE VIRUS OF MICE (MVM) NONSTRUCTURAL PROTEIN NS1 INDUCES NICKING OF MVM DNA AT A UNIQUE SITE OF THE RIGHT-END TELOMERE IN BOTH HAIRPIN AND DUPLEX CONFORMATIONS IN-VITRO, Journal of General Virology, 78, 1997, pp. 2647-2655
The right-end telomere of replicative form (RF) DNA of the autonomous
parvovirus minute virus of mice (MVM) consists of a sequence that is s
elf-complementary except for a th ree nucleotide loop around the axis
of symmetry and an interior bulge of three unpaired nucleotides on one
strand (designated the right-end 'bubble'). This right-end inverted r
epeat can exist in the form of a folded-back strand (hairpin conformat
ion) or in an extended form, base-paired to a copy strand (duplex conf
ormation), We recently reported that the right-end telomere is process
ed in an A9 cell extract supplemented with the MVM nonstructural prote
in NS1. This processing is shown here to result from the NS1-dependent
nicking of the complementary strand at a unique position 21 nt inboar
d of the folded-back genomic 5' end, DNA species terminating in duplex
or hairpin configurations, or in a mutated structure that has lost th
e right-end bulge, are all cleaved in the presence of NS1, indicating
that features distinguishing these structures are not prerequisites fo
r nicking under the in vitro conditions tested, Cleavage of the hairpi
n structure is followed by strand-displacement synthesis, generating t
he right-end duplex conformation, while processing of the duplex struc
ture leads to the release of free right-end telomeres, In the majority
of molecules, displacement synthesis at the right terminus stops a fe
w nucleotides before reaching the end of the template strand, possibly
due to NS1 which is covalently bound to this end. A fraction of the r
ight-end duplex product undergoes melting and re-folding into hairpin
structures (formation of a 'rabbit-ear' structure).