GO:0102263 tRNA-dihydrouridine17 synthase activity

GO:0102263, tRNA-dihydrouridine17 synthase activity, is a molecular_function term in the Gene Ontology that describes the enzymatic reduction of uracil at position 17 of a tRNA molecule to 5,6-dihydrouracil, using NAD(P)H as the reducing agent. This modification is part of the broader family of dihydrouridine (D) modifications that are introduced post-transcriptionally into tRNA and are critical for tRNA structure and function. The term is defined by the reaction: a 5,6-dihydrouracil17 in tRNA + NAD(P) = H+ + a uracil17 in tRNA + NAD(P)H, as curated in QuickGO. Researchers study this activity because site-specific tRNA modifications influence translation fidelity, tRNA stability, and cellular stress responses. The human genome encodes several dihydrouridine synthase (DUS) enzymes, including DUS1L, DUS2, DUS3L, and DUS4L, which are predicted or demonstrated to catalyze D formation at distinct tRNA positions. Understanding GO:0102263 therefore requires integrating enzymology, RNA modification mapping, and functional genomics. The importance of this term extends beyond basic tRNA biology: mutations or expression changes in DUS enzymes have been observed in cancer and neurodevelopmental contexts, making GO:0102263 a relevant node for disease research. However, the field still lacks comprehensive, site-resolved maps of dihydrouridine in human tRNA, and the precise tRNA substrates of each DUS enzyme remain incompletely defined. This article synthesizes the current knowledge of GO:0102263, its catalytic mechanism, associated genes, and the experimental models used to study it.

GO:0102263 describes the catalytic activity of an enzyme that converts a uracil residue at position 17 of a tRNA molecule into 5,6-dihydrouracil17, while oxidizing NAD(P)H to NAD(P)+ and releasing a proton. In other words, it is an NAD(P)H-dependent reductase that modifies tRNA at a specific site, thereby altering the chemical nature of the nucleobase. This activity is distinct from other dihydrouridine synthases that act at different tRNA positions, because the GO term explicitly specifies position 17. The reaction is reversible in principle, but under physiological conditions it likely favors dihydrouridine formation to maintain tRNA modification levels.

GO:0102263 is important because dihydrouridine modification at tRNA position 17 can influence the local structure of the tRNA elbow region, which is critical for tRNA recognition by aminoacyl-tRNA synthetases and translation factors. Alterations in this activity may affect global translation efficiency and fidelity, and have been linked to human diseases such as cancer and neurological disorders. Studying this activity helps clarify how cells fine-tune translation under stress and how tRNA modification defects contribute to pathology.

The following genes encode enzymes or associated factors that are directly or indirectly linked to tRNA-dihydrouridine17 synthase activity (GO:0102263) and related tRNA modification pathways.

The activity of tRNA-dihydrouridine17 synthase is likely regulated at multiple levels, including enzyme expression, cofactor availability, and substrate tRNA abundance. NAD(P)H levels reflect cellular metabolic state, so the reaction may be sensitive to redox balance. tRNA modification enzymes can also be regulated by stress-responsive pathways, though specific regulators of DUS enzymes remain poorly defined. Additionally, the availability of specific tRNA substrates and the competition with other modification enzymes may influence the efficiency of dihydrouridine17 formation.

Dysregulation of tRNA modification enzymes, including dihydrouridine synthases, has been observed in various cancers. Altered DUS expression may affect translation of oncogenes or tumor suppressors, contributing to tumor progression. Targeting tRNA modification pathways is an emerging therapeutic strategy.

Mutations in tRNA modification enzymes cause neurological disorders such as intellectual disability and neurodegeneration. DUS3L and other DUS family members may play roles in neuronal function through tRNA modification. Defects in dihydrouridine formation could impair translation in neurons, which are highly sensitive to protein synthesis defects.

Mitochondrial tRNA modifications are essential for mitochondrial translation. DUS4L is predicted to modify mitochondrial tRNA, and its dysfunction may contribute to mitochondrial disease. Understanding GO:0102263 in mitochondria could reveal new disease mechanisms.

Techniques such as mass spectrometry and RNA sequencing-based methods (e.g., DM-tRNA-seq) can detect dihydrouridine at single-nucleotide resolution. These methods are essential to confirm the specific tRNA substrates of GO:0102263.

Ribo-seq measures translation efficiency and can reveal codon-specific defects when dihydrouridine17 formation is impaired. It is used to link tRNA modification changes to global protein synthesis.

Mass spectrometry-based proteomics can identify changes in protein expression and post-translational modifications upon DUS perturbation. It helps uncover downstream pathways affected by tRNA modification defects.

Genome-wide CRISPR screens can identify synthetic lethal interactions and modifiers of DUS enzyme function. They are powerful for discovering genes that buffer against loss of GO:0102263 activity.

Researchers studying tRNA-dihydrouridine17 synthase activity-related genes often need to determine whether a candidate gene is causally involved in tRNA modification, translation, or disease. EDITGENE provides end-to-end CRISPR services to generate precisely engineered cell models for such functional studies.

GO:0102263, tRNA-dihydrouridine17 synthase activity, represents a specific enzymatic step in tRNA modification that is essential for proper tRNA function and translation. Although the exact human enzymes and their tRNA substrates require further mapping, the DUS family and related modification enzymes are clearly linked to cancer, neurological disorders, and mitochondrial disease. Continued research using CRISPR models and advanced RNA modification mapping will clarify the mechanistic and pathological roles of this activity. Targeting GO:0102263-related pathways may offer new therapeutic opportunities in diseases driven by translation dysregulation.