Semliki Forest Virus Expression System


The Semliki Forest virus (SFV) expression system utilises the efficient replication of SFV to transiently express foreign proteins in eukaryotic cells. In the basic version, cells are infected with a recombinant SFV where the part of the viral ribonucleic acid (RNA) genome that encodes the virus structural proteins is replaced by a gene of interest (transgene). On infection the viral genome is amplified and efficiently translated in the host cell cytoplasm, resulting in high‐level expression of the transgene. Recombinant virus is produced by co‐transfection of recombinant viral genomes and a helper genome that provides the virus structural proteins. Alternatively, infection is initiated by transfection with viral RNA genomes produced in vitro. Further developments, aiming for vaccine and therapeutic applications, include a deoxyribonucleic acid (DNA) vector where the recombinant SFV genome is placed under a cytomegalovirus promoter. This allows transgene expression without involving the structural virus proteins, and avoids RNA work in vitro.

Key Concepts:

  • A polylinker is a short DNA sequence containing multiple unique restriction sites.

  • A packaging signal is a motif in the viral genome that specifically interacts with the capsid forming protein of the virus. This will ensure efficient genome incorporation.

  • Replicon RNA is self‐replicating RNA that directs efficient production of protein.

  • Recombinant SFV is a suicide virus that infect cells and delivers replicon RNA but cannot produce new virions.

  • An autoprotease is a single use enzyme that is synthesised as part of a polyprotein and will release itself from the growing polypeptide chain.

Keywords: alphavirus; protein production; mammalian cells; virus‐like particle; vector RNA; replicon

Figure 1.

Replication of Semliki Forest virus.

Figure 2.

Outline of the Semliki Forest virus expression system.



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Further Reading

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Lundstrom K (2012b) Generation of recombinant alphaviral vectors. Cold Spring Harbor Protocols 2012(7): 825–831. doi:10.1101/pdb.prot070151.

Lundstrom K (2012c) Purification and concentration of alphavirus. Cold Spring Harbor Protocols 2012(7): 832–834. doi:10.1101/pdb.prot070169.

Sjöberg M and Garoff H (2006) Growth of Semliki Forest Virus. In: Celis JE (ed.) Cell Biology: A Laboratory Handbook, 3rd edn, vol. 1, pp. 419–423. London, UK: Elsevier Academic Press.

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Sjöberg, Mathilda(Jul 2014) Semliki Forest Virus Expression System. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0002661.pub3]