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Amino-terminal sequence analysis of alphavirus polypeptides
Abstract:
The single late 26S mRNA of Semliki Forest virus (SFV) directs the synthesis of the four viral structural proteins, C, E3, E2, and E1, and the recently described nonstructural protein, 6K. We report here partial NH2-terminal amino acid sequences of the SFV polypeptides E3 and 6K and of p62, the precursor to E3 and E2. In addition, were have determined a partial NH2-terminal sequence of the Sindbis virus homolog of 6K, the 4.2K protein. p62 and E3 of SFV have identical NH2-terminal amino acid sequences. Comparison of the partial NH2-terminal sequences of 6K of SFV and 4.2K of Sindbis virus with the deduced amino acid sequence encoded by the 26S mRNA of each virus reveals that the genes for these peptides are located in each case between those for E2 and E1. The order of the genes on the 26S mRNA of the alphaviruses is therefore 5'-C-E3-E2-6K-E1-3'. We discuss two mechanisms by which the nascent viral glycoproteins may be inserted into the membrane of the endoplasmic reticulum.
Insights
Semliki Forest virus (SFV) and Sindbis virus gene order was determined. The 6K protein gene is located between the E2 and E1 genes on the 26S mRNA.
Area of Science:
- Virology
- Molecular Biology
- Genetics
Background:
- The single late 26S mRNA of Semliki Forest virus (SFV) encodes multiple viral structural and nonstructural proteins.
- Understanding the gene order and protein relationships is crucial for deciphering viral replication mechanisms.
Purpose of the Study:
- To determine the precise gene order of proteins encoded by the 26S mRNA of Semliki Forest virus (SFV).
- To identify the location of the nonstructural 6K protein gene within the viral genome.
- To compare gene organization with related alphaviruses like Sindbis virus.
Main Methods:
- Partial NH2-terminal amino acid sequencing of SFV polypeptides E3, 6K, and p62 (precursor to E3 and E2).
- Sequencing of the Sindbis virus homolog of 6K, the 4.2K protein.
- Comparison of determined amino acid sequences with deduced sequences from viral 26S mRNA.
Main Results:
- Identical NH2-terminal amino acid sequences were found for p62 and E3 of SFV.
- The genes for SFV 6K and Sindbis virus 4.2K proteins are located between the genes for E2 and E1.
- The gene order on the 26S mRNA of alphaviruses was established as 5'-C-E3-E2-6K-E1-3'.
Conclusions:
- The gene order 5'-C-E3-E2-6K-E1-3' is conserved in alphaviruses.
- This finding clarifies the genomic organization and protein synthesis pathway.
- The study provides insights into mechanisms of viral glycoprotein insertion into the endoplasmic reticulum membrane.