# tRNA Processing

> **NIH NIH R01** · UNIVERSITY OF ROCHESTER · 2022 · $444,138

## Abstract

ABSTRACT
 tRNAs are highly evolved in all organisms for specific recognition by cognate tRNA synthetases, high
fidelity decoding, efficient use in translation, and high stability. The ubiquitous tRNA modifications are highly
conserved in eukaryotes, and many have crucial roles in the yeast Saccharomyces cerevisiae and in human
health. Modifications in the tRNA body (outside the anticodon loop) are crucial for tRNA stability in yeast, and
associated with several neurological disorders in humans. We study the rapid tRNA decay (RTD) pathway in S.
cerevisiae, which targets a subset of mature tRNAs lacking any of several body modifications, due to exposure
of the 5' end to the 5'-3' exonucleases Rat1 and Xrn1. RTD also frequently occurs in tRNA variants with
destabilizing mutations exposing the 5' end, and is inhibited in met22Δ mutants due to increased levels of
adenosine 3',5' bis-phosphate (pAp) and its inhibition of Rat1 and Xrn1.
 Little is known about RTD or the biology of body modifications in any other eukaryote. To address this, we
are studying these processes in the fission yeast Schizosaccharomyces pombe because of its ~600 million
years evolutionary distance from S. cerevisiae, and because of its facile genetics and molecular biology.
 We have recently uncovered an unusual decay pathway in S. cerevisiae in which pre-tRNAs are degraded
in the cytoplasm by a pathway regulated by Met22. This Met22-regulated pre-tRNA decay (MPD) pathway is
independent of RTD, because unlike classical RTD, it does not require the Rat1 or Xrn1 exonucleases and
does not act on mature tRNA, and it is novel because it is also independent of the nuclear surveillance tRNA
decay pathway, which acts in the nucleus on pre-tRNAs through Trf4, RRP6 and the nuclear exosome. Rather,
MPD occurs on unspliced pre-tRNA that accumulates in the cytoplasm due to impaired intron-exon structure.
 We also study modifications in the anticodon loop, due to their importance in translation, with a focus on
Trm7, which 2’-O-methylates N32 and N34 in the anticodon loop of certain tRNAs. S. cerevisiae and S. pombe
trm7 mutants have severe growth defects, while humans with mutations have intellectual disability. Our prior
results showed that the growth defect of S. cerevisiae and S. pombe trm7 mutants was due to reduced
function, but not reduced amounts, of tRNAPhe. We recently discovered an unusual property of S. cerevisiae
and S. pombe trm7Δ mutants: each mutant robustly activates the general amino acid control (GAAC)
response, which massively reprograms gene expression in all eukaryotes due to uncharged tRNA sensed by
Gcn2 kinase, but trm7Δ mutants do not exhibit a detectable tRNA charging defect.
 To follow up, we will: 1) Examine similarities and differences in the RTD pathway and body modification
biology in S. pombe 2) Define how Met22-regulated pre-tRNA decay of anticodon stem variants occurs in S.
cerevisiae 3) Define how trm7Δ mutants activate the GAAC pathway and how Trm7 recogniz...

## Key facts

- **NIH application ID:** 10318630
- **Project number:** 5R01GM052347-27
- **Recipient organization:** UNIVERSITY OF ROCHESTER
- **Principal Investigator:** Eric M. Phizicky
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $444,138
- **Award type:** 5
- **Project period:** 1995-05-01 → 2023-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10318630

## Citation

> US National Institutes of Health, RePORTER application 10318630, tRNA Processing (5R01GM052347-27). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10318630. Licensed CC0.

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