Biology Reference
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VP1-pentamer
VP2
VP3
Minichromosome
30 nm
50 nm
Fig. 3. Components of the SV40 virion. SV40 minor capsid protein VP2
or VP3 bind to one VP1-pentamer from inside the particle. SV40 virus
genome arranges minichromosome with histone and is located at the center
of the particle. Minichromosome inside the particle is thought to take on a
spherical, 30 nm structure in diameter, without histone HI molecule.
Virion Assembly
One VP1-pentamer associates with one VP2 or the amino terminally
truncated form VP3 soon after their synthesis in the cytoplasm
(Fig. 4). It is because both capsid proteins harbor resident nuclear
localization signals (NLSs), 10,11 that an NLS-defective SV40 VP3 can
localize in the nucleus if wild-type VP1 with a functional NLS is
coexpressed in the same cell, suggesting that VP1 and VP3 form a
complex in the cytoplasm prior to nuclear entry. Also, regardless of
the amount of capsid protein synthesized in the cytoplasm, a con-
stant ratio of VP1 and VP3 that reflects the ratio in the mature virion
is found in the nucleus, 12 implying that the stoichiometry of VP1 and
 
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