eIF2D promotes 40S ribosomal subunit recycling during intrinsic ribosome destabilization

Although eukaryotic initiation factor 2D (eIF2D) is implicated in translation initiation, reinitiation, and ribosome recycling, its precise role remains unclear. Here, we show that eIF2D promotes 40S ribosome recycling during intrinsic ribosome destabilization (IRD), a process in which ribosomes stochastically destabilize while translating proteins with consecutive acidic amino acids at their NH2-terminus. Unrecycled 40S ribosomes accumulate in eIF2D-deficient cells, leading to 80S ribosome stalling. Selective translation complex profiling (TCP-seq) reveals that eIF2D preferentially associates with IRD-prone regions. The winged helix domain, unique to eIF2D but absent in MCTS1-DENR, enhances its binding to 40S subunits, but likely clashes with ABCE1 during stop-codon-associated recycling. Loss of eIF2D reduces the expression of IRD-inducing proteins, including splicing factors. Together, these findings define a previously unappreciated role for eIF2D in 40S recycling and clarify its mechanistic divergence from the MCTS1-DENR complex.