An interaction between eIF4A3 and eIF3g drives the internal initiation of translation

Area of Science:

• Molecular Biology
• RNA Biology
• Gene Expression Regulation

Background:

• Internal translation initiation is crucial for protein synthesis.
• Circular RNAs (circRNAs) are increasingly recognized for their role in internal translation.
• The precise mechanisms governing internal translation initiation in circRNAs are not fully understood.

Purpose of the Study:

• To elucidate the molecular mechanisms of internal translation initiation in circRNAs.
• To identify key protein factors involved in circRNA-mediated translation.
• To investigate the role of the exon-junction complex (EJC) in circRNA translation.

Main Methods:

• Protein-protein interaction assays to identify binding partners of eIF4A3.
• In vitro translation assays using synthesized circRNAs.
• Transcriptome-wide analysis of polysomal association of endogenous circRNAs.
• Western blot analysis to detect protein expression.

Main Results:

• eIF3g, a subunit of the eIF3 complex, was identified as a binding partner of eIF4A3.
• The interaction between eIF4A3 and eIF3g acts as a molecular linker, facilitating internal ribosomal entry.
• eIF4A3 drives internal translation from circRNAs in an eIF3g-dependent manner.
• Efficient polysomal association of endogenous circRNAs requires eIF4A3.
• A subset of circRNAs can express full-length proteins, such as β-catenin, dependent on eIF4A3.

Conclusions:

• The eIF4A3-eIF3g interaction is a critical determinant for internal translation initiation on circRNAs.
• eIF4A3 plays a significant role in the translation of endogenous circRNAs.
• This study expands the understanding of the protein-coding potential of circRNAs and the human transcriptome.