Reovirus hemagglutinin mRNA codes for two polypeptides in overlapping reading frames.

Area of Science:

• Molecular Biology
• Virology
• Protein Synthesis

Background:

• The human reovirus S1 mRNA is known to encode the viral hemagglutinin protein.
• Gene expression can sometimes yield multiple protein products from a single mRNA transcript through alternative initiation or reading frames.

Purpose of the Study:

• To identify and characterize any previously unrecognized polypeptides produced from the human reovirus S1 mRNA.
• To determine the initiation site and genetic basis for the synthesis of this novel polypeptide.

Main Methods:

• In vitro translation using reticulocyte and wheat germ extracts.
• Hybrid-arrest of translation assays with cloned S1 DNA restriction fragments.
• NH2-terminal sequence analysis of the synthesized polypeptide.
• Analysis of viral-infected mouse L cell extracts.

Main Results:

• A novel 14-kDa polypeptide was synthesized in vitro from human reovirus S1 mRNA.
• Hybrid-arrest experiments and NH2-terminal sequencing revealed that the 14-kDa polypeptide initiates at the second AUG codon.
• The coding sequence for the 14-kDa polypeptide is located within the hemagglutinin gene but in a distinct reading frame.
• The 14-kDa polypeptide was detected in virus-infected mouse L cells, though not in purified virions.

Conclusions:

• Human reovirus S1 mRNA directs the synthesis of two distinct proteins: hemagglutinin and a 14-kDa polypeptide.
• The 14-kDa polypeptide originates from a different reading frame within the S1 gene, initiated at the second AUG.
• This novel polypeptide is produced during viral infection in host cells, suggesting a potential biological role.