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Measles virus phosphoprotein retains the nucleocapsid protein in the cytoplasm
M Huber1, R Cattaneo, P Spielhofer
1Institut für Molekularbiologie I, Universität Zürich.
Abstract:
Measles virus (MV) proteins were efficiently expressed in COS and Vero cells from vectors based on the strong cytomegalovirus enhancer-promoter and the simian virus 40 origin of replication. When expressed alone, nucleocapsid protein (N) migrates predominantly into the nucleus whereas phosphoprotein (P) is located in the cytoplasm. Coexpression of N and P proteins results in retention of the N protein in the cytoplasm, as seen also in infected cells. The retention of N protein is due to specific interactions with the P protein since coexpression of N with either the matrix or the hemagglutinin protein had no effect. Mapping of the regions of N-P interactions on P protein revealed that the carboxy-terminal 40% of P was sufficient for specific binding to N; however, the carboxy-terminal 60% of P was required for retention of N in the cytoplasm. Thus, the V and C proteins encoded within the first half of the P gene are not involved in the cytoplasmic retention of N protein. N protein might be fortuitously targeted to the nucleus as a result of its many basic amino acids, presumably destined to interact with the MV genome. However, this set of experiments has allowed to analyze in vivo the interactions between the N and P proteins.
Insights
Measles virus (MV) nucleocapsid (N) protein is retained in the cytoplasm when coexpressed with phosphoprotein (P), indicating specific N-P interactions. This interaction is crucial for MV replication dynamics.
Area of Science:
- Virology
- Molecular Biology
- Cell Biology
Background:
- Measles virus (MV) is a significant human pathogen.
- Understanding the intracellular localization and interactions of MV proteins is key to deciphering viral replication mechanisms.
Purpose of the Study:
- To investigate the intracellular localization of measles virus nucleocapsid (N) and phosphoprotein (P).
- To elucidate the interaction between N and P proteins and its effect on N protein localization.
Main Methods:
- Efficient expression of MV proteins in COS and Vero cells using CMV enhancer-promoter and SV40 origin vectors.
- Analysis of protein localization via coexpression studies.
- Mapping of protein interaction domains.
Main Results:
- Expressed alone, N protein localizes to the nucleus, while P protein localizes to the cytoplasm.
- Coexpression of N and P proteins results in cytoplasmic retention of N protein, mimicking infected cells.
- Specific interaction between N and P proteins mediates N retention in the cytoplasm.
- The C-terminal 60% of P protein is required for N cytoplasmic retention, while the C-terminal 40% mediates binding.
Conclusions:
- The interaction between measles virus N and P proteins is essential for regulating N protein localization.
- The cytoplasmic retention of N protein by P protein is a specific interaction, not mediated by other MV proteins like matrix or hemagglutinin.
- The V and C proteins encoded within the P gene are not involved in this N retention mechanism.