ELAC1 Repairs tRNAs Cleaved during Ribosome-Associated Quality Control

Summary: Ribosome-associated quality control (RQC) disassembles aberrantly stalled translation complexes to recycle or degrade the constituent parts. A key step of RQC is the cleavage of P-site tRNA by the endonuclease ANKZF1 (Vms1 in yeast) to release incompletely synthesized polypeptides from ribosomes for degradation. Re-use of the cleaved tRNA for translation requires re-addition of the universal 3′CCA nucleotides removed by ANKZF1. Here, we show that ELAC1 is both necessary and sufficient to remove the 2′,3′-cyclic phosphate on ANKZF1-cleaved tRNAs to permit CCA re-addition by TRNT1. ELAC1 activity is optimized for tRNA recycling, whereas ELAC2, the essential RNase Z isoform in eukaryotes, is required to remove 3′ trailers during tRNA biogenesis. Cells lacking ELAC1 specifically accumulate unrepaired tRNA intermediates upon the induction of ribosome stalling. Thus, optimal recycling of ANKZF1-cleaved tRNAs in vertebrates is achieved through the duplication and specialization of a conserved tRNA biosynthesis enzyme. : Yip et al. identify ELAC1 as a tRNA repair enzyme that is necessary and sufficient to remove 2′,3′-cyclic phosphates from tRNAs cleaved by ANKZF1 on stalled ribosomes to permit 3′CCA re-addition and tRNA recycling. Keywords: tRNase Z, ribosome stalling, ELAC1, 2’,3’-cyclic phosphate, tRNA processing