Baculovirus Vector-Baculovirus is a rod shape virus infecting invertebrate including insect cells. Post infection, virus is either released as free virions or many virus particles are trapped in a protein complex known as polyhedron. The protein responsible for trapping virus into polyhedron is polyhydrin and it help in transmission of virus from one host to other. The polyhydrin is not important for virus propagation but it is under very strong promoter to produce the protein in large quantities. Realizing this fact, replacement of polyhydrin gene with a foreign DNA fragment will allow expression of protein in large quantities. The baculovirus Autographa californica multiple nuclear polyhedrosis virus (AcMNPV) is used as a vector to express protein. The transfer vector map of AcMNPV is given in Figure 19.3. The gene of interest will be inserted into the cloning site placed adjacent to the promoter. It has polyhedron termination sequence down-stream to the cloning site to stop transcription of cloned gene. More details of over-expression strategies will be discussed in future lecture.

Figure 19.3:  Structural elements of a baculovirus transfer vector.

Mammalian Vector- large number of excellent mammalian vectors are in circulation to clone eukaryotic gene for protein synthesis and study the transcription mechanism. A generalized scheme with the structural elements required to design mammalian vector is given in Figure 19.4. As discussed earlier, it contains a eukaryotic replication of origin from an animal virus such as SV40 from simian virus 40. A promoter to drive the expression of foreign gene and selection marker, other eukaryotic features such as polyadenylation, transcription termination site etc.