Cap-proximal nucleotides via differential eIF4E binding and alternative promoter usage mediate translational response to energy stress

Transcription and translation are highly energy consuming processes and both are modulated by the intracellular energy status. Transcription start site (TSS) selection and alternative promoter (AP) usage contribute to the complexity of gene expression but little is known about their impact on translation in response to metabolic deficiencies. Here we performed TSS mapping of the translatome following energy stress. We assessed the contribution of cap-proximal TSS nucleotides and strikingly found dramatic effect on translation only upon stress. As eIF4E levels were reduced, we analyzed its binding to capped-RNAs with different initiating nucleotides and found differential affinity, the lowest being for 5’cytidine, in correlation with the translational response. In addition the number of differentially translated APs was highly elevated following energy stress, suggesting that AP usage is central to the stress response. These include novel glucose-starvation-induced downstream promoters for the translation regulators eIF4A and Pabp which are translationally-induced despite the general translational inhibition. The resultant eIF4A protein is N-terminally truncated and acts as eIF4A inhibitor. The induced Pabp isoform has shorter 5'UTR removing an auto-inhibitory element. These findings uncovered several levels of coordination of transcription and translation responses to energy stress. Cap-seq of RNA from three polysomal fractions in control and glucose starvaion (GS) conditions, in two replicates