Cap-snatching mechanism in yeast L-A double-stranded RNA virus

Area of Science:

• Virology
• Molecular Biology
• Biochemistry

Background:

• Eukaryotic mRNA requires a 5' cap structure (m(7)GpppX-) for stability and translation.
• Influenza virus employs a cap-snatching mechanism using viral polymerase to acquire capped mRNA fragments.
• Yeast double-stranded RNA totivirus L-A also utilizes cap-snatching for its transcripts.

Purpose of the Study:

• To elucidate the unique cap-snatching mechanism employed by the yeast totivirus L-A.
• To identify the viral components and processes involved in L-A's mRNA capping.
• To compare L-A's cap-snatching with known mechanisms, such as influenza's.

Main Methods:

• In vitro biochemical assays to study the capping reaction.
• Site-directed mutagenesis of the L-A Gag protein (His154 to Arg154).
• Analysis of viral transcript synthesis and expression in vivo.

Main Results:

• L-A transfers only the m(7)Gp moiety from the cap donor, preserving the triphosphate linkage in viral transcripts.
• His154 of the Gag protein is crucial for the in vitro capping reaction, forming an m(7)Gp-His adduct.
• The Arg154 mutation significantly impaired in vivo capping and expression of viral transcripts, confirming Gag's role.

Conclusions:

• The yeast totivirus L-A utilizes a distinct cap-snatching mechanism involving its structural protein Gag, not the polymerase.
• This mechanism differs from influenza virus by transferring only m(7)Gp.
• The findings suggest convergent evolution with cellular guanylyltransferases and demonstrate the adaptability of eukaryotic RNA viruses.