Transient expression in insect cells using a recombinant baculovirus synthesising bacteriophage T7 RNA polymerase

Transient expression systems based on recombinant viruses have proved useful for in situ studies on post-translational modification and trafficking of proteins, protein/protein and protein/nucleic acid interactions. More recently, transient transcription and expression has been used for reverse genetic studies on RNA viruses (1-3). In particular, the expression system based on recombinant vaccinia virus synthesising bacteriophage T7 RNA polymerase (VTF7-3) has proved popular (4). In this system, cassettes containing the target genes under the control of an upstream T7 promoter are placed into plasmids or the genome of vaccinia virus for transfection or coinfection into cells infected with VTF7-3. The VTF7-3 based transient expression system has been modified in several ways to improve its versatility (5). The baculovirus expression system also provides a method for synthesising recombinant proteins at very high levels in