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Measles virus polypeptides in infected cells studied by immune precipitation and one-dimensional peptide mapping
Abstract:
Measles virus does not turn off host cell polypeptide synthesis, making it difficult to precisely identify the polypeptides specified by the virus during the infectious cycle. By using the technique of immune precipitation with measles-specific antisera, the host cell background has been eliminated, and new observations have been made concerning measles virus polypeptides H, P, NP, F, and M. The H polypeptide is first synthesized as a monomer which is processed by further glycosylation and by the formation of disulfide-bonded dimers. Polypeptide P (70,000 daltons) has been found to occur also as a 65,000-dalton molecule, P2, and both forms of the molecule are equally phosphorylated. Polypeptide NP is processed from a cleavage-sensitive form (which undergoes cleavage during the process of isolation to form polypeptide 6 [41,000 daltons]) to a form which is resistant to this cleavage. The fusion and hemolysin polypeptide is first found in the cells as a 55,000-dalton precursor, F0, which is clearly resolved from the NP polypeptide on gel electrophoresis. The measles virus F0 protein identified in previous reports had not been resolved from the 60,000-dalton NP polypeptide. The M protein occurs in the infected cells as two distinct bands, and, as in the case of Sendai virus, one of these two M protein bands represents a phosphorylated form of the other.
Insights
Measles virus research identified key viral polypeptides, including H, P, NP, F, and M, using immune precipitation. This technique clarified their synthesis, processing, and modifications, advancing our understanding of measles virus replication.
Area of Science:
- Virology
- Molecular Biology
- Immunology
Background:
- Host cell protein synthesis complicates identification of viral polypeptides during measles infection.
- Immune precipitation is crucial for distinguishing viral proteins from host cell background.
Purpose of the Study:
- To identify and characterize measles virus-specified polypeptides.
- To elucidate the synthesis, processing, and post-translational modifications of viral proteins H, P, NP, F, and M.
Main Methods:
- Immune precipitation using measles-specific antisera.
- Gel electrophoresis to analyze polypeptide size and modifications.
- Analysis of protein synthesis and processing during the infectious cycle.
Main Results:
- Identified and characterized measles virus polypeptides H, P, NP, F, and M.
- Described the monomeric synthesis and dimerization of H polypeptide.
- Characterized the dual forms (70-kDa and 65-kDa P2) of P polypeptide, both equally phosphorylated.
- Detailed the processing of NP polypeptide from a cleavage-sensitive to a cleavage-resistant form.
- Resolved the F0 precursor (55-kDa) from NP polypeptide, clarifying previous ambiguities.
- Observed M protein in two distinct bands, one representing a phosphorylated form.
Conclusions:
- Immune precipitation effectively isolates measles virus polypeptides for detailed study.
- Elucidated the distinct processing and modification pathways for key measles virus proteins.
- Provided a clearer understanding of measles virus protein synthesis and its implications for viral replication.