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Is there a role for actin in virus budding?
Abstract:
Electrophoretic data from both sodium dodecyl sulfate-polyacrylamide gels (SDS-PAGE) and acid-urea gels reveal a protein in purified murine mammary tumor virus (MuMTV) which co-migrates with purified chick skeletal muscle actin. 125I-labeling of intact and disrupted virus preparations shows that the actin-like protein is not artifactually adsorbed to the outside of virions during isolation. Quantitative SDS-PAGE and examination of negatively stained preparations show that the actin cannot be accounted for by a contaminating population of virus-free vesicles. The ultrastructure of mammary epithelial cells and of Rous sarcoma virus-transformed chick embryo fibroblasts shows that virus extrusion is associated with filament-containing cellular processes. In particular, MuMTV is released from the ends of long microvilli which contain a bundle of 6-8-nm microfilaments and share other structural features with intestinal microvilli. We suggest that virus nucleoids require an interaction with host cell contractile proteins for their extrusion from the cell.
Insights
Murine mammary tumor virus (MuMTV) contains an actin-like protein, not from contamination. This protein may interact with host cell contractile proteins for virus extrusion from microvilli.
Area of Science:
- Virology
- Cell Biology
- Biochemistry
Background:
- Murine mammary tumor virus (MuMTV) is an oncogenic retrovirus.
- The mechanism of retroviral extrusion from host cells is not fully understood.
Purpose of the Study:
- To investigate the protein composition of purified MuMTV.
- To explore the potential role of host cell proteins in MuMTV release.
Main Methods:
- Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and acid-urea gel electrophoresis.
- 125I-labeling of virus preparations.
- Negative staining electron microscopy.
- Ultrastructural analysis of infected cells.
Main Results:
- A protein co-migrating with chick skeletal muscle actin was identified in purified MuMTV.
- 125I-labeling confirmed the actin-like protein is an intrinsic viral component.
- Quantitative analysis ruled out contamination by vesicles.
- MuMTV extrusion was observed at the tips of microvilli containing microfilaments.
Conclusions:
- MuMTV contains an actin-like protein.
- Virus release is associated with cellular microvilli containing microfilaments.
- Host cell contractile proteins may be involved in MuMTV nucleoid extrusion.