Dhh1 and Pat1 play a role in translational repression and reinitiation under iron deficiency in yeast

Abstract

Iron is an essential micronutrient for all eukaryotes, required as a cofactor for fundamental biological processes, including protein synthesis. Iron depletion causes extensive reprogramming of gene expression and a complex translational response. While global repression of translation under iron scarcity has largely been attributed to TORC1 inhibition and Gcn2 mediated phosphorylation of eIF2α, the involvement of additional post transcriptional regulators has remained unclear. In this report, we uncover that the DEAD box helicase Dhh1 and the decapping activator Pat1 are key regulators of the translational reprogramming that occurs during iron starvation. Polysome profiling shows that the deletion of DHH1 or PAT1 attenuates the reduction in translation after prolonged iron deficiency, and that both proteins act within the same pathway. In contrast, Dhh1 acts independently of the Gcn2 pathway. We further reveal an unexpected role of Dhh1 and Pat1 in the generation of 3′UTR derived translation products, a phenomenon associated with a reduced activity of the essential protein Rli1 during iron-limited conditions. Loss of either factor greatly diminishes the appearance of these reinitiation-derived peptides, while Gcn2 does not appear to be involved in this process. Notably, RLI1 transcripts levels are elevated in a dhh1Δ mutant, suggesting that Dhh1 contributes to RLI1 mRNA downregulation under iron deficiency. Altogether, our results situate Dhh1 and Pat1 as central regulators of the translational response to iron starvation, coordinating both repression of initiation and downstream reinitiation events.