QTMAN (queuosine-tRNA mannosyltransferase) is a glycosyltransferase that catalyzes the mannosylation of queuosine at position 34 in cytoplasmic tRNA(Asp) 1. The enzyme specifically attaches an α-mannose moiety to the allylic 3-hydroxyl group of the cyclopentene ring of queuosine(34), generating mannosyl-queuosine(34) with precise chemical specificity 12. This modification functions to slow elongation rates at cognate codons (GAC and GAU) during translation, thereby regulating protein synthesis efficiency 1. Beyond translational control, QTMAN-mediated mannosylation contributes to cellular proteostasis by reducing protein aggregation 1. The biological significance of QTMAN extends to vertebrate development; zebrafish qtman knockout lines exhibit shortened body length, indicating that mannosyl-queuosine modification is essential for post-embryonic growth 1. Recent evidence suggests associations between aberrant tRNA queuosine glycosylation and human diseases including cancer and inflammatory and neurological disorders 3. QTMAN represents a conserved mechanism for fine-tuning protein synthesis through tRNA modification, with implications for metabolic regulation and developmental processes in vertebrates.