Eukaryotic translation initiation factor 4G (eIF4G) coordinates interactions with eIF4A, eIF4B and eIF4E in binding and translation of the barley yellow dwarf virus 3' cap-independent translation element (BTE) [RNA]

Barley yellow dwarf virus (BYDV) RNA, lacking a 5′ cap and a 3′poly(A) tail, contains a cap-independent translation element (BTE) in the 3′untranslated region that interacts with host translation initiation factor eIF4G. To determine how eIF4G recruits the mRNA, three eIF4G deletion mutants were constructed: (i) eIF4G601-1196, containing amino acids 601-1196, including the putative BTE-binding region, and binding domains for eIF4E, eIF4A, eIF4B; (ii) eIF4G601-1488, which contains an additional C-terminal eIF4A-binding domain; and (iii) eIF4G742-1196, which lacks the eIF4E-binding site. eIF4G601-1196 binds BTE tightly and supports efficient translation. The helicase complex, consisting of eIF4A, eIF4B and ATP, stimulated BTE binding with eIF4G601-1196 but not eIF4G601-1488, suggesting that the eIF4A binding domains, may serve a regulatory role, with the C-terminal binding site having negative effects. eIF4E binding to eIF4G601-1196, induced a conformational change, significantly increasing the binding affinity to BTE. A comparison of the binding of eIF4G deletion mutants with BTEs containing mutations, showed a general correlation between binding affinity and ability to facilitate translation. In summary, these results reveal a new role for the helicase complex in 3′ CITE-mediated translation and show that the functional core domain of eIF4G, plus an adjacent probable RNA binding domain mediate translation initiation.

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