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Fig. 1
Different SFV vectors. (
a
) Replication-defi cient vector system. (
b
) Replication-
competent vector. (
c
) DNA-layered vector.
Blue triangles
represent subgenomic
SFV 26S promoter;
yellow triangle
represents DNA II polymerase promoter
the expression vector, the generated virus particles are rendered
replication defi cient, which allows one round of infection. It will
generate high transient expression of the gene of interest in the
infected cells.
(b) Replication-competent vectors
contain the full-
length viral genome and an additional subgenomic promoter and
the gene of interest. Application of these vectors will generate both
recombinant protein expression and new virus progeny.
(c) DNA-
layered vectors
are expression vectors with the viral replicase genes
and the gene of interest including an upstream DNA polymerase
type II promoter, which allows direct delivery of plasmid DNA for
transient expression. The use of DNA-layered vectors eliminates
any production of infectious particles and thereby generates no
potential biohazard. However, the effi cient infection of a broad
range of host cells provided by viral particles is lost and gene delivery
is restricted to transfection methods.
Alphavirus vectors and particularly SFV vectors have been
applied for the expression of topologically different proteins [
4
,
8
].
Proteins known to be diffi cult to express such as membrane proteins
have been expressed at high levels from SFV vectors [
9
,
10
]. In this
context, a structural genomics approach was conducted for the
expression of more than 100 G protein-coupled receptors (GPCRs)
[
11
,
12
]. The high expression levels of GPCRs encouraged large-
scale production for structural biology [
11
,
13
].
The broad host range of alphavirus vectors has allowed expres-
sion studies in a number of cell lines and primary cell cultures. In
this context, the effi cient transduction of neuronal cells has ren-
dered alphaviruses excellent tools for neurobiology. The high
infection rate of 90 % of primary neurons in culture has provided
effi cient expression of various genes [
14
]. It has been possible to
study functional activity and localization of GPCRs and ion chan-
nels in alphavirus-infected neurons. Moreover, injection of SFV
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