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Matrix protein of Akv murine leukemia virus: genetic mapping of regions essential for particle formation
E C Jørgensen1, F S Pedersen, P Jørgensen
1Department of Molecular Biology, University of Aarhus, Denmark.
Abstract:
Type C retroviruses assemble at the plasma membrane of the infected cell. Attachment of myristic acid to the N terminus of the Gag precursor polyprotein has been shown to be essential for membrane localization and virus morphogenesis. Here, we report that the matrix (MA) protein contains regions that in conjunction with myristylation are important for Gag protein stability and the assembly of murine leukemia viruses. We identified these domains by generating a series of Akv murine leukemia virus mutants carrying small in-frame deletions within the coding region of the MA protein encompassing 129 amino acids. Studies show that mutants with deletions within the segment encoding the first 102 amino acids were all replication defective, whereas the C-terminal residues 103 to 124 seem not to have any critical function in virus maturation. Cells expressing the replication-defective genomes did not release any detectable Gag proteins. In one mutant, deletion of 3 amino acids in the N terminus resulted in an inefficiently myristylated, stable Gag polyprotein. The remaining defect genomes encoded unstable Gag proteins, although they were modified with myristic acid. The results suggest that the matrix domain plays an important role in stabilizing the Gag polyprotein.
Insights
The matrix (MA) protein is crucial for stabilizing Gag polyproteins in murine leukemia viruses. Specific N-terminal regions of MA, along with myristylation, are essential for virus assembly and replication.
Area of Science:
- Virology
- Molecular Biology
- Retroviral Assembly
Background:
- Type C retroviruses, including murine leukemia viruses, assemble at the host cell's plasma membrane.
- Myristic acid attachment to the Gag precursor polyprotein's N-terminus is vital for membrane localization and virus morphogenesis.
Purpose of the Study:
- To investigate the role of the matrix (MA) protein in the stability and assembly of murine leukemia viruses.
- To identify specific domains within the MA protein that, in conjunction with myristylation, influence Gag protein stability and viral replication.
Main Methods:
- Generation of Akv murine leukemia virus mutants with in-frame deletions in the MA protein coding region (129 amino acids).
- Analysis of replication defects, Gag protein stability, and myristylation status in mutant viruses.
- Assessment of Gag protein release from infected cells.
Main Results:
- Deletions within the first 102 amino acids of MA resulted in replication-defective viruses lacking detectable Gag protein release.
- Mutants with deletions in C-terminal residues (103-124) showed no critical defects in virus maturation.
- A mutant with a 3-amino acid N-terminal deletion exhibited inefficient myristylation but a stable Gag polyprotein.
- Other replication-defective mutants encoded unstable Gag proteins despite myristylation.
Conclusions:
- The matrix (MA) domain of murine leukemia viruses plays a critical role in stabilizing the Gag polyprotein.
- Specific N-terminal regions of the MA protein are essential for Gag protein stability and viral replication, working in concert with myristylation.