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Virus-specific proteins synthesized in cells infected with RNA+ temperature-sensitive mutants of Sindbis virus
Abstract:
All Sindbis virus temperature-sensitive mutants defective in "late" functions were systematically surveyed by acrylamide-gel electrophoresis for similarities and differences in the intracellular pattern of virus-specific proteins synthesized at the permissive and nonpermissive temperatures. Only cells infected with mutants of complementation group C showed an altered pattern. At the nonpermissive temperature, these mutants failed to induce the synthesis of a polypeptide corresponding to the nucleocapsid protein and instead overproduced a protein of higher molecular weight than either viral structural protein. This defect was shown to be irreversible by the finding that (3)H-leucine incorporated at 41.5 C specifically failed to appear in the nucleocapsid of virions subsequently released at 29 C. Attempts to demonstrate a precursor protein in wild-type infections were inconclusive.
Insights
Temperature-sensitive Sindbis virus mutants revealed that group C mutants fail to produce nucleocapsid protein at nonpermissive temperatures. This defect is irreversible, impacting viral protein synthesis and virion assembly.
Area of Science:
- Virology
- Molecular Biology
- Protein Synthesis
Background:
- Sindbis virus is a well-studied alphavirus model.
- Temperature-sensitive (ts) mutants are crucial for dissecting viral replication cycles.
- Understanding viral protein synthesis is key to controlling viral infections.
Purpose of the Study:
- To systematically analyze Sindbis virus temperature-sensitive mutants.
- To identify defects in viral protein synthesis at the nonpermissive temperature.
- To characterize the specific molecular defect in mutants affecting late viral functions.
Main Methods:
- Acrylamide-gel electrophoresis was used to analyze intracellular viral proteins.
- Temperature shifts (permissive to nonpermissive) were employed.
- Radioactive labeling with (3)H-leucine tracked protein incorporation.
- Complementation analysis grouped mutants based on functional defects.
Main Results:
- Mutants in complementation group C exhibited an altered protein synthesis pattern at nonpermissive temperatures.
- These mutants failed to synthesize the nucleocapsid protein.
- A higher molecular weight protein was overproduced instead of the nucleocapsid protein.
- The defect in nucleocapsid protein synthesis was irreversible, confirmed by labeling studies.
Conclusions:
- Sindbis virus complementation group C mutants are defective in nucleocapsid protein synthesis.
- This defect is irreversible and occurs at the nonpermissive temperature.
- The findings suggest a critical role for this gene product in nucleocapsid formation and viral assembly.