Figure 1: Various types of SFV vectors used for heterologous gene expression. (A) Replication-competent vector: Full-length genome of SFV with an additional SFV 26S subgenomic promoter ( ) upstream of the foreign gene of interest. This vector system generates replication-proficient particles, which after infection produces new progeny and recombinant protein. (B) Replication-deficient vector: In this system, expression and helper vectors are co-electroporated in parallel to generate replication-deficient particles due to the packaging of only RNA carrying the packaging signal (PS). Infection results in recombinant protein expression, but no virus progeny. (C) DNA layered vector: The presence of a CMV promoter (?) allows direct use of plasmid DNA for cell transfection to generate recombinant protein.