Sl. Spence et Jm. Pipas, SIMIAN-VIRUS 40 LARGE T-ANTIGEN HOST-RANGE DOMAIN FUNCTIONS IN VIRIONASSEMBLY, Journal of virology, 68(7), 1994, pp. 4227-4240
The simian virus 40 (SV40) T antigen host range mutants dl1066 and dl1
140 display a postreplicative block to plaque formation which suggests
a novel role for T antigen late in the viral life cycle. The host ran
ge mutants. dl1066 and dl1140 are able to grow in and plaque on BSC bu
t not on CV1 monkey kidney cells, a normally permissive host. Previous
work showed that in CV1 cells infected with dl1066 and dl1140, levels
of viral DNA replication and of late capsid protein accumulation were
only slightly reduced and the failure to accumulate agnoprotein was n
ot likely to be the major factor responsible for the mutants' growth d
efect. Here we show that the host range mutants are defective in the a
ssembly of viral particles. SV40 assembly proceeds as the progressive
conversion of 75S viral chromatin complexes to 200S-240S assembled vir
ions. When virus infected cell extracts are separated on 5 to 40% sucr
ose gradients, wild-type extracts show the greatest accumulation of vi
ral late protein in the 200S-240S fractions corresponding to the assem
bled virus peak and lesser amounts in the 75S-150S fractions correspon
ding to immature assembly intermediates. The host range mutants dl1066
and dl1140 grown in nonpermissive CV1 cells, however, failed to assem
ble any appreciable amounts of mature 200S-240S virions and accumulate
75S intermediates, whereas in permissive BSC cells, levels of assembl
y were more slightly reduced than those of the wild type. Analysis of
the protein composition of gradient fractions suggests that SV40 assem
bly proceeds by a mechanism similar to that proposed for polyomavirus
and suggests that the host range blockage may result from a failure of
such mutants to add VP1 to 75S assembly intermediates.