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Hepatitis A virus polyprotein synthesis initiates from two alternative AUG codons
M Tesar1, S A Harmon, D F Summers
1Department of Cellular, Viral, and Molecular Biology, University of Utah School of Medicine, Salt Lake City 84132.
Virology
|February 1, 1992
Summary
Hepatitis A virus uses a downstream AUG codon for protein synthesis, but either start site can function. The 5
Area of Science:
- Virology
- Molecular Biology
- Genetics
Background:
- Hepatitis A virus (HAV) genomic RNA encodes a large polyprotein.
- Two potential translation initiation sites (AUG codons) exist for HAV polyprotein synthesis.
- The specific in vitro and in vivo usage of these initiation sites remains unclear.
Purpose of the Study:
- To determine which of the two AUG codons is preferentially used for HAV translation.
- To investigate the influence of the 5' untranslated region (5'UTR) on translation initiation site selection.
Main Methods:
- Site-directed mutagenesis to independently eliminate each AUG start codon.
- In vitro translation assays using modified and unmodified viral RNA transcripts.
- Cell transfection assays (BS-C-1 cells) with modified and unmodified viral RNA.
Main Results:
- Preferential usage of the downstream AUG codon (positions 741-743) was observed in vitro and in vivo.
- Either start codon could be utilized when the other was absent.
- Deletion of the 5'UTR led to equal utilization of both AUG sites in vitro, indicating its regulatory role.
Conclusions:
- The downstream AUG codon is the primary initiation site for hepatitis A virus translation.
- The 5' untranslated region plays a crucial role in directing ribosomal entry to specific internal initiation sites.
- Both initiation sites can support productive viral infections, but their usage is modulated by the 5'UTR.