Pestivirus translation initiation occurs by internal ribosome entry

Area of Science:

• Virology
• Molecular Biology
• Genetics

Background:

• Pestiviruses, including bovine viral diarrhea virus (BVDV), possess a 5' noncoding region (NCR) crucial for genome translation.
• Understanding the translational mechanisms of BVDV is key to comprehending pestivirus replication and pathogenesis.

Purpose of the Study:

• To investigate the role of the BVDV 5' NCR in initiating translation of the viral genome.
• To identify specific sequences and structures within the 5' NCR that regulate translation.

Main Methods:

• In vitro translation assays using RNA transcripts containing the BVDV 5' NCR and reporter genes.
• Hybrid-arrest translation studies with specific oligonucleotides targeting the 5' NCR.
• Dicistronic expression vectors and transfection into BHK cells to assess translation efficiency.

Main Results:

• A 20-kDa polypeptide (p20) was synthesized in vitro using BVDV 5' NCR RNA, indicating translation initiation.
• A stem-loop structure (nucleotides 154-261) and the initiating AUG (nucleotide 386) were critical for p20 synthesis.
• Deletion of nucleotides 173-236 in the 5' NCR significantly reduced reporter gene expression in vitro and in transfected cells.

Conclusions:

• The BVDV 5' NCR functions as an internal ribosome entry site (IRES) for cap-independent translation initiation.
• This IRES-mediated translation mechanism in BVDV is analogous to that observed in Hepatitis C Virus (HCV).
• These findings highlight the close evolutionary relationship between pestiviruses and hepaciviruses within the Flaviviridae family.