Previous studies have shown that expression of the vesicular stomatiti
s virus (VSV) glycoprotein (G) from a Semliki Forest virus (SFV) RNA r
eplicon results in the production of propagating infectious particles
that we call minimal viruses. These minimal viruses consist of vesicle
s containing VSV G protein that bud from the plasma membrane and trap
the infectious SVF, G RNA, but they do not contain other viral structu
ral proteins. The cell binding and membrane fusion activity of the VSV
G protein allow minimal viruses to propagate in tissue culture cells.
To determine if these minimal viruses could be used to express foreig
n genes, we added a second SFV promoter and a multiple cloning site do
wnstream of the VSV G gene. We report here expression of three differe
nt proteins from this modified, minimal virus vector. Although express
ion of each foreign, unselected gene was lost rapidly from the vector
upon passaging, it was possible after the initial transfection to deri
ve stocks of infectious particles that could be used to infect multipl
e additional cultures and transfer protein expression efficiently. Whe
n cells were infected with these minimal viruses, host protein synthes
is was shut off and the foreign protein and VSV G proteins were the ma
jor proteins expressed in the infected cells. Both were expressed at s
imilar levels and accumulated to about 1-2% of total cell protein. (C)
1996 Academic Press, Inc.