ATP-Independent Initiation during Cap-Independent Translation of m6A-Modified mRNA

The methylation of adenosine in the N⁶ position (m⁶A) is a widely used modification of eukaryotic mRNAs. Its importance for the regulation of mRNA translation was put forward recently, essentially due to the ability of methylated mRNA to be translated in conditions of inhibited cap-dependent translation initiation, e.g., under stress. However, the peculiarities of translation initiation on m⁶A-modified mRNAs are not fully known. In this study, we used toeprinting and translation in a cell-free system to confirm that m⁶A-modified mRNAs can be translated in conditions of suppressed cap-dependent translation. We show for the first time that m⁶A-modified mRNAs display not only decreased elongation, but also a lower efficiency of translation initiation. Additionally, we report relative resistance of m⁶A-mRNA translation initiation in the absence of ATP and inhibited eIF4A activity. Our novel findings indicate that the scanning of m⁶A-modified leader sequences is performed by a noncanonical mechanism.