Biology Reference
In-Depth Information
binding studies have suggested that all three capsid proteins bind
DNA nonspecifically, raising the dilemma of how they attain speci-
ficity to the SV40 minichromosome in the presence of a large excess
of genomic DNA.
14-18
VP3 has been shown to repress transcription
from the viral early promoter
in vitro
, and that it cooperated with Sp1
through the Sp1 binding site on viral genome.
19-21
Therefore, Sp1
might recruit the VP1-pentamer-VP2/3 complex to minichromo-
some, conferring upon them specific DNA recognition. After associ-
ation of VP1-pentamer to minichromosome, the carboxy terminus of
VP1 responsible for the non-equivalent association of capsomeres
interacts with the adjacent VP1-pentamer to form SV40 capsid.
22
During viral infection, the 72 KDa cellular chaperone heat shock
cognate protein (hsc70) binds VP1 post-translation and colocalizes
with VP1 to the nucleus.
23
Recombinant VP1 C-terminal domain
from
E. coli
was copurified with the prokaryotic hsp70 chaperone
DnaK. A member of the 70 kDa family of the cellular stress pro-
teins assist in protein folding by preventing inappropriate intra- and
intermolecular interactions during normal protein synthesis and trans-
port and when the cells are exposed to a variety of environmental
stresses. This suggests a role of the 70 kDa heat shock protein (hsp70)
for the chaperones to regulate the quality and location of capsid assem-
bly. In particle formation
in vitro
, particle assembly was promoted by
the eukaryotic hsc70 protein, in combination with the J-domain func-
tion of the SV40 large T-antigen protein.
24
Thus, polyomavirus cap-
sid assembly can be recapitulated with high-fidelity
in vitro
, using
either prokaryotic or eukaryotic hsp70 chaperone systems, thereby
supporting a role of cellular chaperones in the
in vivo
regulation of
virion assembly. It also revealed that VP2 allowed particle assembly
of VP1-pentamers into spherical particles in a pH range of 7.0 to 4.0
in vitro
.
25
A region common to VP2 and VP3 (amino acids 119-272)
was required to promote the VP1-pentamer assembly. These results
are relevant to the control of recombinant capsid formation by minor
capsid proteins. After particle formation, virions escape from the
infected cells with cell lysis
26-30
or without cell lysis from apical cell
surface.
31
