Updated publication reference for PubMed record(s): 33166396. The Mtq2-Trm112 methyltransferase is known to modify the translational eukaryotic release factor eRF1 on the glutamine side chain of a universally conserved GGQ motif, which is essential to translation termination. The exact role of eRF1 methylation remains unknown. As the deletion of MTQ2 leads to severe growth impairment in S. cerevisiae, we have investigated its role further. Here we report an unexpected function of Mtq2 in ribosome biogenesis. We reveal that Mtq2 is part of nuclear precursor ribosomes to 60S subunits, and we demonstrate that its catalytic activity is required for the stable production of mature 5.8S and 25S rRNAs and for pre-60S export. Consistently, in the absence of Mtq2 function pre-60S subunits enriched in the export factors Nmd3 and Arx1 accumulate in the nucleus. We conclude that, in addition to its role as a translation terminator modification enzyme, Mtq2 is a ribosome assembly factor which is important for late-stage large ribosomal subunit formation.