M. Pawlita et al., DNA ENCAPSIDATION BY VIRUS-LIKE PARTICLES ASSEMBLED IN INSECT CELLS FROM THE MAJOR CAPSID PROTEIN VP1 OF B-LYMPHOTROPIC PAPOVAVIRUS, Journal of virology, 70(11), 1996, pp. 7517-7526
Capsids of polyomaviruses-small, nonenveloped DNA viruses-consist of t
he major structural protein VP1 and the minor structural proteins VP2
and VP3, The contributions of the individual capsid proteins to functi
ons of the viral particle, such as DNA encapsidation, cell receptor at
tachment, entry, and uncoating, are still not clear, Here we show that
viruslike particles assembled in nuclei of insect cells from VP1 of t
he monkey B-lymphotropic papovavirus (LPV) are sufficient to unspecifi
cally encapsidate DNA. LPV VP1 expressed in large amounts in insect ce
lls by a baculovirus vector assembled spontaneously in the nuclei to f
orm viruslike particles, After metrizamide equilibrium density gradien
t purification and nuclease digestion, a fraction of these particles w
as shown to contain VP1-associated linear, double-stranded DNA with a
predominant size of 4.5 kb, The fraction of DNA-containing VP1 particl
es increased with time and dose of baculovirus vector infection, The D
NA-containing particles, further purified by sucrose gradient centrifu
gation, appeared as ''full'' particles in negative-staining electron m
icroscopy, As shown by DNA hybridization, the encapsidated DNA consist
ed of insect cell and baculoviral sequences with no apparent strong ho
mology to LPV sequences, Three non-LPV VP1-derived host proteins with
apparent molecular masses of approximately 14, 15, and 16 kDa copurifi
ed with the DNA-containing particles and may represent insect cell his
tones encapsidated together with the DNA, A similar species of host DN
A was also found in purified LPV wild-type virions, These data suggest
that LPV VP1 alone can be sufficient to encapsidate linear DNA in a s
equence-independent manner.