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Preformed cytoplasmic nucleocapsids are not necessary for alphavirus budding
K Forsell1, G Griffiths, H Garoff
1Department of Bioscience at Novum, Huddinge, Sweden.
The EMBO Journal
|December 2, 1996
Summary
Alphavirus assembly models are challenged by new findings. Semliki Forest virus mutants lacking cytoplasmic nucleocapsid (NC) assembly still budded efficiently, suggesting NC preassembly is not required for alphavirus budding.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- The established model for alphavirus assembly, using Semliki Forest virus (SFV) as an example, posits cytoplasmic nucleocapsid (NC) formation prior to budding at the plasma membrane (PM).
- Preformed NCs are believed to serve as templates for viral envelope organization during budding.
Purpose of the Study:
- To investigate the role of cytoplasmic NC assembly in alphavirus morphogenesis.
- To characterize SFV deletion mutants with altered NC assembly pathways.
Main Methods:
- Introduction of deletions in the linker peptide of the SFV capsid protein.
- Characterization of viral particle assembly and budding efficiency in deletion mutants.
- Analysis of nucleocapsid (NC) formation in cytoplasm versus at the plasma membrane (PM).
Main Results:
- Two SFV deletion mutants were characterized, exhibiting defects in cytoplasmic NC assembly.
- These mutants formed NCs at the PM concurrently with virus budding.
- Despite altered morphogenesis, mutants produced near wild-type (wt) efficiency of infectious viral particles.
- Spike-capsid interactions at the PM are suggested to rescue the NC assembly defect.
Conclusions:
- Cytoplasmic preassembly of nucleocapsids (NCs) is not a prerequisite for alphavirus budding.
- Alternative morphogenesis pathways exist for alphavirus assembly.
- SFV morphogenesis shares similarities with type D and C retroviruses.