Dengue and Zika Virus 5' Untranslated Regions Harbor Internal Ribosomal Entry Site Functions

Area of Science:

• Virology
• Molecular Biology
• Genetics

Background:

• Flaviviruses, including Dengue virus (DENV) and Zika virus (ZIKV), are significant human pathogens.
• Flavivirus translation is typically cap-dependent, utilizing a 5'-terminal capping group.
• Previous research suggested DENV RNA might not strictly require a cap for translation.

Purpose of the Study:

• To investigate the translational control mechanisms of DENV and ZIKV.
• To determine if the 5' untranslated regions (5'-UTRs) of DENV and ZIKV possess internal ribosomal entry site (IRES) competence.
• To explore the implications of IRES activity for flavivirus biology and evolution.

Main Methods:

• Assessed the translation of uncapped monocistronic mRNAs with DENV or ZIKV 5'-UTRs in BHK and C6/36 cells.
• Evaluated the ability of DENV/ZIKV 5'-UTRs to drive downstream gene expression in bicistronic constructs in BHK cells.
• Correlated IRES competence with the observed infectivity of uncapped DENV/ZIKV genomic transcripts in mammalian and mosquito cells.

Main Results:

• Uncapped mRNAs with DENV or ZIKV 5'-UTRs efficiently directed reporter gene translation in both BHK and C6/36 cells.
• DENV/ZIKV 5'-UTRs induced downstream gene expression in BHK cells but not in C6/36 cells when placed in bicistronic constructs.
• Uncapped DENV/ZIKV genomic transcripts initiated infection in both mammalian (BHK) and mosquito (C6/36) cells.

Conclusions:

• The 5'-UTRs of DENV and ZIKV exhibit IRES competence, enabling cap-independent translation.
• This IRES activity provides an alternative strategy for gene expression, independent of the cap-dependent mechanism.
• The findings raise significant questions about flavivirus evolution, biology, and potential new control strategies for flavivirus diseases.