eIF4G functionally differs from eIFiso4G in promoting internal initiation, cap-independent translation, and...

Area of Science:

• Molecular Biology
• Plant Biochemistry
• Gene Expression Regulation

Background:

• Eukaryotic initiation factor (eIF) 4G is crucial for ribosome binding to mRNA during translation initiation.
• Plants possess two eIF4G homologs, eIF4G and eIFiso4G, which form distinct complexes, eIF4F and eIFiso4F.
• These homologs share limited sequence identity, suggesting potential functional specialization.

Purpose of the Study:

• To investigate the functional differences between plant eIF4G and eIFiso4G proteins within their respective complexes (eIF4F and eIFiso4F).
• To determine how these complexes differentially regulate mRNA translation, particularly concerning mRNA structure and cap dependence.

Main Methods:

• Comparative analysis of translation efficiency mediated by eIF4F and eIFiso4F.
• Assessment of 5'-cap dependency and poly(A)-binding protein requirement for translation.
• Testing translation of mRNAs with varying 5' secondary structures (unstructured vs. structured) and cap status (capped, uncapped, monocistronic, dicistronic).

Main Results:

• Both eIF4F and eIFiso4F require poly(A)-binding protein for optimal translation, with cap stimulation inversely correlated to complex concentration.
• While both complexes translate unstructured mRNAs, eIF4F significantly outperforms eIFiso4F in translating mRNAs with 5'-proximal secondary structures.
• eIF4F demonstrates a greater ability to stimulate translation from uncapped and multi-cistronic mRNAs compared to eIFiso4F.

Conclusions:

• Plant eIFiso4F and eIF4F have diverged functions in mRNA translation.
• eIFiso4F preferentially promotes translation of unstructured mRNAs.
• eIF4F exhibits broader translational capability, supporting structured, uncapped, and multi-cistronic mRNAs, potentially compensating for inhibited cap-dependent translation.