Scope and mechanism of eIF4F-independent mRNA translation

In eukaryotic cells, protein synthesis typically begins with the binding of eIF4F to the 7-methylguanylate (m7G)cap found on the 5' end of the majority of mRNAs. Surprisingly, overall translational output remains robust under eIF4F inhibition. The sustained protein synthesis has been largely attributed to cap-independent translation mediated by internal ribosome entry sites (IRES). However, the IRES-driven translation is substrate-specific and largely incompatible with the broad spectrum of eIF4F-resistant translatomes.Here, we report that N6-methyladenosine (m6A)-mediated translation prevails on capped mRNAs and is resistant to eIF4F inactivation.Depletion of the methyltransferase METTL3 selectively inhibits translation of mRNAs bearing 5'UTR methylation, but not mRNAs with 5' terminal oligopyrimidine (TOP) elements. Mechanistically, we identify ABCF1 as a critical mediator of m6A-promoted translation under both stress and physiological conditions. Supporting the role of ABCF1 in m6A-mediated cap-independent translation, ABCF1-sensitive transcripts largely overlap with METTL3-responsible mRNA targets. By illustrating the scope and the mechanism of translation initiation that is neither cap- nor IRES-dependent, these findingsreshape our current perceptions of cellular translational pathways Overall design: Ribo-seq and RNA-seq in Scramble, ABCF1 and METTL3 knockdown.