# tRNA Modification: Types, Functions, and Mechanisms ## Introduction to tRNA Modification Transfer RNA (tRNA) is the adapter molecule that decodes messenger RNA (mRNA) codons into the [amino acid sequence](/blog/guides/amino-acid-sequence) of a protein. While the canonical cloverleaf structure of tRNA is well known, a critical layer of complexity exists beyond the four standard ribonucleotides: tRNA modification. This refers to the post-transcriptional chemical alteration of specific nucleosides within the tRNA molecule. These modifications are not rare exceptions; they are pervasive. On average, a single tRNA molecule contains between 7 and 15 modified nucleosides, and across all organisms, over 100 distinct chemical modifications have been identified. The modification of tRNA is a fundamental aspect of RNA biology that directly impacts the accuracy, efficiency, and regulation of protein synthesis. ### What Are tRNA Modifications? A tRNA modification is a covalent chemical change to a standard ribonucleotide (adenosine, guanosine, cytidine, or uridine) after it has been incorporated into the tRNA transcript. These changes can be as simple as the addition of a single methyl group or as complex as the installation of a multi-ring hypermodified base. The modified nucleosides are found throughout the tRNA molecule, but they are particularly concentrated in two critical regions: the anticodon loop and the TΨC arm. The modification process is catalyzed by a diverse group of enzymes known as tRNA-modifying enzymes, which recognize specific tRNA substrates and install the correct chemical group at the correct position. The resulting modified nucleosides have distinct names and abbreviations, such as pseudouridine (Ψ), 5-methyluridine (m⁵U), and N⁶-threonylcarbamoyladenosine (t⁶A). For a comprehensive catalog of these structures, see [Modified Bases in tRNA](/knowledge/molecular-biology/modified-bases-in-trna). ### Why Are They Important? The importance of tRNA modifications cannot be overstated. They are essential for the structural integrity of the tRNA molecule, ensuring it folds into its correct three-dimensional L-shape. More critically, modifications in the anticodon loop directly influence codon-anticodon interactions, affecting both the fidelity (accuracy) and the speed of translation. Modifications in the tRNA body, such as those in the TΨC arm, contribute to thermal stability and protect the tRNA from degradation by nucleases. Without these modifications, tRNAs are often unstable, misfolded, or unable to decode codons accurately. The functional consequences of losing tRNA modifications are severe, ranging from growth defects in yeast to severe neurological and mitochondrial disorders in humans. ## Types of tRNA Modifications The chemical diversity of tRNA modifications is vast. They can be broadly categorized into several classes based on the type of chemical change. Understanding these categories is essential for grasping how they exert their functional effects. ### Methylation Methylation is the most common type of tRNA modification. It involves the addition of a methyl group (-CH₃) to various positions on the base or the ribose sugar. Methylation can occur on the nitrogen or carbon atoms of the purine or pyrimidine rings, or on the 2'-hydroxyl group of the ribose. - **Base Methylation:** This includes modifications like 1-methyladenosine (m¹A), 5-methylcytidine (m⁵C), and N⁷-methylguanosine (m⁷G). For example, m¹A at position 58 of the TΨC arm is found in nearly all tRNAs and is critical for maintaining the tertiary structure of the tRNA. The enzyme Trm6/Trm61 complex in yeast catalyzes this reaction. m⁵C at position 38 in the anticodon loop of certain tRNAs is catalyzed by the enzyme Trm4 (NSUN2 in humans) and is important for translation fidelity. - **Ribose Methylation:** This involves the methylation of the 2'-hydroxyl group of the ribose, producing 2'-O-methylnucleosides (e.g., Cm, Um, Gm). This modification protects the tRNA from alkaline hydrolysis and increases the hydrophobicity of the RNA, which can stabilize local structures. The 2'-O-methylation at position 32 in the anticodon loop is common and is catalyzed by the Trm7 enzyme in yeast. ### Pseudouridylation Pseudouridylation is the isomerization of uridine to pseudouridine (Ψ). This is a unique modification because it involves breaking the N1-C1' glycosidic bond and re-forming a new C5-C1' bond. This results in a nucleoside where the uracil base is attached to the ribose via a carbon-carbon bond instead of a nitrogen-carbon bond. This change creates an extra hydrogen bond donor on the N1 position of the base, which can participate in additional base-stacking interactions and hydrogen bonding with water molecules. Pseudouridine is often referred to as the "fifth nucleotide" due to its abundance. It is found at several positions in tRNA, most notably at position 55 in the TΨC loop, which is a hallmark of nearly all tRNAs. The enzyme responsible for this is pseudouridine synthase 1 (Pus1) in yeast. Pseudouridylation at position 55 is critical for the structural stability of the tRNA elbow region and for its interaction with the ribosome. ### Thiolation Thiolation is the addition of a sulfur atom to a base, most commonly uridine, converting it to a thiouridine derivative. The most well-known thiolated modification is 2-thiouridine (s²U), which is found at the wobble position (position 34) of tRNAs that decode codons ending in A or G for specific amino acids like lysine, glutamic acid, and glutamine. The presence of the sulfur atom at the C2 position of uridine has a profound effect on the base-pairing properties of the nucleoside. It restricts the conformational flexibility of the ribose, favoring the C3'-endo sugar pucker. This conformation locks the base into a position that preferentially pairs with adenine rather than guanine, thereby preventing misreading of near-cognate codons. The thiolation of tRNA in bacteria is catalyzed by the enzyme MnmA, which uses a cysteine desulfurase (IscS) to provide the sulfur atom. In humans, the corresponding enzyme is CTU1/CTU2. ### Other Modifications Beyond methylation, pseudouridylation, and thiolation, there are numerous other complex modifications, often referred to as hypermodified nucleosides. - **Queuosine (Q):** This is a complex modification found at the wobble position of tRNAs for asparagine, aspartic acid, histidine, and tyrosine. It is a 7-deazaguanosine derivative that is synthesized in bacteria and acquired by higher eukaryotes through their diet. Queuosine is thought to modulate the speed and fidelity of translation in response to cellular stress. - **Wyosine (yW) and Derivatives:** These are complex tricyclic modifications found at position 37 (3' adjacent to the anticodon) of tRNA^Phe. They are critical for maintaining the reading frame during translation by preventing frameshifting. The enzyme Tyw1 in yeast is involved in its synthesis. - **Threonylcarbamoyladenosine (t⁶A):** This is a hypermodified adenosine found at position 37 in tRNAs that decode codons starting with A. It is synthesized by a multi-subunit enzyme complex (KEOPS in eukaryotes, TsaC/TsaD in bacteria). The t⁶A modification is essential for the proper recognition of the codon start and for preventing frameshifting. ## The tRNA Modification Process The process of installing a modification onto a tRNA is a highly specific and regulated enzymatic event. It requires the coordinated action of modifying enzymes, precise recognition of the target tRNA, and correct timing relative to transcription and other processing steps. ### Enzymes Involved tRNA-modifying enzymes are a diverse group of proteins that can be classified based on the type of reaction they catalyze. They include methyltransferases, pseudouridine synthases, thiolases, and more complex ligases. These enzymes often require cofactors. For example, methyltransferases use S-adenosylmethionine (SAM) as the methyl group donor. Thiolases require a sulfur donor, which is often provided by a cysteine desulfurase. The KEOPS complex, which synthesizes t⁶A, requires ATP and threonine as substrates. Many of these enzymes are highly conserved from bacteria to humans, underscoring their fundamental importance. For instance, the Trm1 enzyme, which catalyzes the dimethylation of guanosine at position 26 (m²₂G), is found in all domains of life. In humans, mutations in the gene encoding Trm1 (TRMT1) are associated with intellectual disability. ### Recognition Mechanisms How do these enzymes recognize their specific target sites among the ~75 nucleotides of a tRNA? The recognition mechanisms are varied and can involve: 1. **Primary Sequence Recognition:** Some enzymes recognize a short, specific sequence motif around the target nucleotide. For example, the enzyme that creates m¹A at position 58 recognizes the sequence context in the TΨC loop. 2. **Structural Recognition:** Many enzymes recognize the three-dimensional shape of the tRNA, particularly the L-shaped tertiary structure. They may contact multiple regions of the tRNA that are distant in the primary sequence but close in the folded structure. 3. **Co-factor Proteins:** In some cases, the modifying enzyme requires an accessory protein to help it recognize the correct tRNA. For example, the enzyme that modifies the wobble uridine in bacteria (MnmA) requires a separate protein (MnmE and MnmG) to first modify the position, and then MnmA acts. The specificity is crucial; modifying the wrong nucleotide or the wrong tRNA would be catastrophic for translation. ### Timing of Modification tRNA modifications can occur at different stages of the tRNA life cycle. Most modifications are introduced post-transcriptionally, after the tRNA has been transcribed by RNA polymerase III but often before it is fully processed and exported from the nucleus. - **Co-transcriptional Modifications:** Some modifications, particularly those in the anticodon loop, can occur while the tRNA is still being transcribed. This is more common in bacteria, where [transcription and translation](/knowledge/molecular-biology/transcription-translation) are coupled. - **Post-transcriptional Modifications:** The majority of modifications occur after the full-length pre-tRNA has been synthesized. They can occur in the nucleus before the tRNA is exported to the cytoplasm, or in the cytoplasm after export. For example, the modification of the wobble base (position 34) often occurs in the cytoplasm in eukaryotes, after the tRNA has been fully processed. This spatial and temporal regulation allows the cell to control the modification status of tRNAs in response to environmental cues. ## Functions of tRNA Modifications The functions of tRNA modifications are as diverse as their structures. They play critical roles in every aspect of tRNA biology, from folding and stability to decoding and translation regulation. ### Structural Stabilization The tertiary structure of tRNA is a compact L-shape, formed by interactions between the D-loop and the TΨC loop. Many modifications are critical for stabilizing this structure. - **m¹A at position 58:** This modification is located at the junction of the TΨC and variable loops. It is a positive charge on the base that helps to stabilize the reverse Hoogsteen base pair with the U54 in the TΨC loop. Without m¹A58, the tRNA is thermodynamically less stable and more prone to degradation. - **Pseudouridine at position 55:** The extra hydrogen bond donor of Ψ55 can coordinate a water molecule that bridges the phosphate backbone of the D-loop and the TΨC loop, further stabilizing the elbow region of the tRNA. - **Ribose Methylations:** 2'-O-methylations protect the tRNA from endonucleolytic cleavage by making the phosphodiester bond more resistant to hydrolysis. These structural modifications ensure that the tRNA folds into its correct shape and remains stable at the physiological temperatures of the organism. For thermophilic organisms, a higher density of stabilizing modifications is often observed to maintain tRNA integrity at high temperatures. ### Codon-Anticodon Interaction The most critical function of tRNA modifications is their role in the anticodon loop, specifically at positions 34 (the wobble position) and 37 (3' adjacent to the anticodon). These modifications are essential for accurate and efficient decoding of the mRNA. - **Wobble Position (Position 34) Modifications:** The base at position 34 is the most heavily modified position in tRNA. Modifications here restrict the conformational flexibility of the base, limiting the possible base-pairing partners. For example, the presence of 2-thiouridine (s²U) at position 34 restricts the base to the C3'-endo conformation, which pairs strongly with A but weakly with G. This prevents the tRNA from misreading codons that end in G, thereby increasing translation fidelity. Similarly, inosine (I), which is formed by the deamination of adenosine, can pair with U, C, and A, expanding the decoding capacity of a single tRNA. - **Position 37 Modifications:** The base at position 37 is almost always a purine and is frequently hypermodified. These bulky modifications, such as t⁶A and wyosine, stack on top of the first base of the anticodon (position 36). This stacking interaction stabilizes the codon-anticodon helix and prevents the anticodon from "slipping" during translation. This is critical for maintaining the correct reading frame. The t⁶A modification, for example, is essential for the decoding of all ANN codons and for preventing +1 frameshifting. The interplay between position 34 and position 37 modifications is a fine-tuned system that ensures the ribosome can accurately and rapidly decode the genetic code. The [tRNA Anticodon](/knowledge/molecular-biology/trna-anticodon) is the primary site of this regulatory control. ### Reading Frame Maintenance The ribosome must maintain the reading frame with high precision to avoid producing truncated or non-functional proteins. tRNA modifications play a direct role in this process. - **Preventing Frameshifts:** Modifications at position 37, such as t⁶A and wyosine, are particularly important for preventing frameshifting. They stabilize the codon-anticodon interaction at the P site, preventing the tRNA from slipping forward or backward by one nucleotide. In yeast, loss of t⁶A modification leads to a significant increase in +1 frameshifting. - **Modulating Translation Speed:** Some modifications, such as queuosine, can slow down the rate of translation at specific codons. This pause can be important for co-translational protein folding, giving the nascent polypeptide chain time to fold correctly before the next amino acid is added. ## Methods to Study tRNA Modifications Studying tRNA modifications is technically challenging due to their chemical diversity, the difficulty in distinguishing them from standard nucleosides, and their often substoichiometric nature (not all tRNAs of a given species may be modified at a given position). However, several powerful techniques have been developed. ### Mass Spectrometry Mass spectrometry (MS) is the gold standard for identifying and quantifying tRNA modifications. The workflow typically involves: 1. **Isolation of tRNA:** Total RNA is extracted from cells, and the small RNA fraction (which includes tRNA) is purified, often by size-exclusion chromatography or gel electrophoresis. 2. **Digestion:** The purified tRNA is digested to single nucleosides using a combination of nucleases (e.g., nuclease P1) and phosphatases (e.g., [alkaline phosphatase](/knowledge/molecular-biology/alkaline-phosphatase)). 3. **LC-MS/MS Analysis:** The digested nucleosides are separated by high-performance liquid chromatography (HPLC) and then analyzed by tandem mass spectrometry (MS/MS). The mass-to-charge ratio (m/z) of each nucleoside is measured, and the fragmentation pattern is used to identify the specific modification. For example, a methylated adenosine will have a mass that is 14 Da (the mass of a methyl group) heavier than unmodified adenosine. 4. **Quantification:** By comparing the peak areas of the modified nucleosides to those of standards, the relative abundance of each modification can be quantified. This method is highly sensitive and can detect modifications present at very low levels. ### High-Performance Liquid Chromatography HPLC is often used in conjunction with MS, but it can also be used as a standalone technique for separating and quantifying modified nucleosides. The nucleosides are separated based on their hydrophobicity using a C18 reversed-phase column. The elution profile is monitored by UV absorbance at 254 nm (for bases) or 280 nm (for pseudouridine). Each modified nucleoside has a characteristic retention time and UV spectrum, allowing for its identification. However, HPLC alone is less definitive than MS for identifying novel modifications, as some modifications may have similar retention times. ### Sequencing-Based Methods Traditional RNA sequencing (RNA-seq) cannot detect most tRNA modifications because the reverse transcriptase enzyme reads through them as if they were unmodified bases. However, several specialized sequencing methods have been developed. - **[Nanopore Sequencing](/blog/guides/nanopore-sequencing):** This technology can directly detect modified bases as the RNA molecule passes through a nanopore. The current signature is affected by the chemical nature of the base, allowing for the identification of modifications like pseudouridine and m⁵C. - **Chemical Labeling and RT-Stop:** Some modifications cause reverse transcriptase to pause or stop. For example, m¹A and m³C can be detected by their ability to cause RT-arrest. Other modifications, like pseudouridine, can be specifically labeled with a chemical (e.g., CMC) that then causes an RT-stop, allowing their position to be mapped. - **Antibody-Based Enrichment:** Antibodies specific for certain modifications (e.g., m⁶A) can be used to immunoprecipitate tRNA fragments containing that modification, which are then sequenced. These methods are rapidly evolving and are providing new insights into the dynamic regulation of tRNA modifications. ## Clinical Relevance and Diseases Given the fundamental role of tRNA modifications in translation, it is not surprising that defects in their biosynthesis are linked to a wide range of human diseases. These are often referred to as "tRNA-modification disorders." ### Mitochondrial Diseases Mitochondria have their own genome and their own set of tRNAs, which are essential for the synthesis of the 13 proteins encoded by the mitochondrial DNA. Mutations in mitochondrial tRNA genes or in the nuclear genes encoding mitochondrial tRNA-modifying enzymes are a major cause of mitochondrial disease. - **MELAS (Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes):** This is often caused by a mutation in the mitochondrial tRNA^Leu(UUR) gene. This mutation affects the modification of the wobble base (position 34), specifically the 5-taurinomethyluridine (τm⁵U) modification. The lack of this modification impairs the decoding of UUR codons, leading to a severe defect in mitochondrial protein synthesis. - **MERRF (Myoclonic Epilepsy with Ragged Red Fibers):** This is frequently caused by a mutation in the mitochondrial tRNA^Lys gene, which affects the modification of the wobble base (m¹s²U). This leads to a defect in the translation of mitochondrial proteins, particularly those that are hydrophobic and require a high level of translational accuracy. ### Neurological Disorders The nervous system is highly sensitive to defects in protein synthesis, and tRNA modifications are no exception. Mutations in tRNA-modifying enzymes are increasingly being linked to neurological and neurodevelopmental disorders. - **Intellectual Disability:** Mutations in the *TRMT1* gene, which encodes the enzyme responsible for m²₂G26 modification, cause autosomal recessive intellectual disability. The loss of this modification leads to defects in tRNA stability and translation, particularly in neurons. - **Amyotrophic Lateral Sclerosis (ALS):** Mutations in the *ELP3* gene, which encodes a subunit of the Elongator complex (responsible for the mcm⁵s²U modification of the wobble base), have been linked to ALS. The loss of this modification impairs the translation of proteins rich in specific codons, leading to neuronal dysfunction. - **Bipolar Disorder and Schizophrenia:** Genome-wide association studies have linked variants in genes encoding tRNA-modifying enzymes to an increased risk of these psychiatric disorders, although the exact mechanisms are still under investigation. ### Cancer Cancer cells have altered metabolism and protein synthesis rates. tRNA modifications are emerging as important players in cancer biology. - **NSUN2 (m⁵C Methyltransferase):** NSUN2 is overexpressed in many cancers, including breast, colon, and bladder cancer. It is thought to promote tumorigenesis by stabilizing specific tRNAs and enhancing the translation of oncogenes. Conversely, loss of NSUN2 leads to an accumulation of tRNA fragments (tiRNAs), which can inhibit translation and promote cell death. - **Queuosine Deficiency:** The level of queuosine modification in tRNA is often reduced in cancer cells. This is thought to be due to a deficiency in the dietary precursor (queuine) or an alteration in the enzymes that incorporate it. The hypomodified state is associated with increased [cell proliferation](/blog/guides/cell-proliferation) and a more aggressive tumor phenotype. ## Common Pitfalls and Misconceptions Students often encounter several conceptual difficulties when learning about tRNA modifications. Being aware of these can help avoid confusion. ### tRNA vs mRNA Modifications A common mistake is to conflate tRNA modifications with the more famous mRNA modifications, such as N⁶-methyladenosine (m⁶A). While both are types of [RNA Modification](/knowledge/molecular-biology/rna-modification), they are fundamentally different in their chemistry, location, and function. mRNA modifications are primarily involved in regulating mRNA stability, splicing, and translation, and are often dynamic and reversible. tRNA modifications are more numerous, chemically diverse, and are largely constitutive, playing a structural and decoding role. While some enzymes are shared, the majority are specific to each RNA type. Furthermore, the functional impact of a single tRNA modification is often more severe than a single mRNA modification, as it can abolish the function of an entire tRNA species. ### Essential vs Non-Essential Not all tRNA modifications are essential for life. In yeast, for example, deleting the gene for a single tRNA-modifying enzyme often has no obvious phenotype under standard [laboratory conditions](/knowledge/diagnostics/molecular/laboratory-conditions). This is because many modifications are "fine-tuning" elements that provide a growth advantage only under stress conditions (e.g., high temperature, nutrient limitation). However, some modifications are absolutely essential. For example, the t⁶A modification at position 37 is essential for viability in all organisms tested, as its loss leads to a catastrophic failure of translation. It is important to distinguish between modifications that are critical for the basic function of tRNA and those that are modulatory. ### Dynamic Regulation A third misconception is that tRNA modifications are static and always present at 100% stoichiometry. In reality, the modification status of a tRNA can be dynamic and regulated. The activity of tRNA-modifying enzymes can be regulated by: - **Environmental Stress:** For example, the levels of s²U modification increase under oxidative stress to promote the translation of stress-response proteins. - **Nutrient Availability:** The queuosine modification depends on the availability of queuine in the diet. - **Cell Cycle:** The expression of some tRNA-modifying enzymes is cell-cycle regulated. This dynamic regulation adds another layer of complexity to the control of gene expression and is an active area of research. ## Summary and Key Takeaways tRNA modifications are a fundamental and complex layer of gene regulation. They are not mere decorations but are essential for the structural integrity, stability, and decoding function of tRNA. The diversity of these modifications, from simple methylations to complex hypermodified bases, reflects their varied roles in fine-tuning the translation process. Defects in their biosynthesis lead to a range of severe human diseases, highlighting their clinical importance. The study of tRNA modifications requires sophisticated techniques, and our understanding of their dynamic regulation is still evolving. ## Frequently Asked Questions ### What are tRNA modifications? tRNA modifications are covalent chemical changes made to the standard ribonucleotides (A, U, C, G) of a transfer RNA molecule after it has been transcribed. These changes, catalyzed by specific enzymes, can be simple (like adding a methyl group) or complex (like building a multi-ring structure). They are found throughout the tRNA but are especially concentrated in the anticodon loop and the TΨC arm. ### How many types of tRNA modifications exist? Over 100 distinct tRNA modifications have been identified across all domains of life. They can be broadly classified into groups such as methylations, pseudouridylations, thiolations, and hypermodified bases like queuosine and wyosine. A single tRNA molecule typically contains 7 to 15 of these modifications. ### What is the process of tRNA modification? The process involves a specific tRNA-modifying enzyme recognizing its target tRNA, often by a combination of primary sequence and three-dimensional structure. The enzyme then catalyzes the chemical reaction, using cofactors like S-adenosylmethionine (SAM) for methylation or a sulfur donor for thiolation. Modifications can occur co-transcriptionally or, more commonly, post-transcriptionally, either in the nucleus or the cytoplasm. ### Why are tRNA modifications important? tRNA modifications are critical for several reasons. They stabilize the three-dimensional L-shape of the tRNA, protect it from degradation, and are absolutely essential for accurate and efficient codon-anticodon interactions. Modifications at the wobble position (34) and position 37 ensure correct decoding and maintain the reading frame, preventing frameshift errors. ### What are the most common tRNA modifications? The most common modifications include pseudouridine (Ψ), which is found at position 55 in nearly all tRNAs; 1-methyladenosine (m¹A) at position 58; and various methylations like 5-methylcytidine (m⁵C) and 2'-O-methylnucleosides. In the anticodon loop, modifications like 2-thiouridine (s²U) and N⁶-threonylcarbamoyladenosine (t⁶A) are widespread and critical for function. ### How are tRNA modifications studied? The primary methods are mass spectrometry (MS) and high-performance liquid chromatography (HPLC), which are used to identify and quantify modified nucleosides after digesting the tRNA. Newer sequencing-based methods, such as [nanopore sequencing](/blog/guides/nanopore-sequencing) and chemical-labeling approaches, are also being developed to map modifications to specific positions on the tRNA. ### Can tRNA modifications cause disease? Yes. Mutations in genes encoding tRNA-modifying enzymes or in the tRNA genes themselves that affect modification sites are linked to numerous diseases. These include mitochondrial disorders like MELAS and MERRF, neurological conditions like intellectual disability and ALS, and various types of cancer. The loss of proper modification impairs translation, which is particularly detrimental to high-energy-demanding tissues like the brain and muscle. ## Key Takeaways - tRNA modifications are pervasive and chemically diverse, with over 100 types identified across all organisms. - They are essential for tRNA structural stability, protecting the molecule from degradation and ensuring correct folding. - Modifications in the anticodon loop (positions 34 and 37) are critical for accurate [codon-anticodon pairing](/knowledge/molecular-biology/codon-anticodon) and for maintaining the translational reading frame. - The modification process is highly specific, catalyzed by dedicated enzymes that recognize their tRNA substrates with precision. - tRNA modifications are not static; they can be dynamically regulated in response to cellular stress and environmental conditions. - Defects in tRNA modification pathways are directly linked to a range of human diseases, including mitochondrial disorders, neurological diseases, and cancer. - Studying tRNA modifications requires specialized techniques like mass spectrometry and next-generation sequencing, and this field remains an active area of research. ## Further Reading - Suzuki T. *The expanding world of tRNA modifications and their disease relevance*. Nature reviews. Molecular cell biology. 2021. [PubMed 33658722](https://doi.org/10.1038/s41580-021-00342-0) - Wei FY, Tomizawa K. *tRNA modifications and islet function*. Diabetes, obesity & metabolism. 2018. [PubMed 30230180](https://doi.org/10.1111/dom.13405) - Oerum S et al. *m1A Post-Transcriptional Modification in tRNAs*. Biomolecules. 2017. [PubMed 28230814](https://doi.org/10.3390/biom7010020) - Tuorto F, Lyko F. *Genome recoding by tRNA modifications*. Open biology. 2016. [PubMed 27974624](https://doi.org/10.1098/rsob.160287) - Huang M et al. *METTL1-Mediated m7G tRNA Modification Promotes Lenvatinib Resistance in Hepatocellular Carcinoma*. Cancer research. 2023. [PubMed 36102722](https://doi.org/10.1158/0008-5472.CAN-22-0963) - Chen Y et al. *Mevalonate pathway promotes liver cancer by suppressing ferroptosis through CoQ10 production and selenocysteine-tRNA modification*. Journal of hepatology. 2025. [PubMed 40653112](https://doi.org/10.1016/j.jhep.2025.06.034) ## Related Clinical & Scientific Guides * [MAPK Pathway: Mechanism, Function, and Clinical Relevance](/knowledge/molecular-biology/mapk-pathway) * [Mammalian Cell Culture Bioreactors: A Practical Guide](/knowledge/molecular-biology/mammalian-cell-culture-bioreactor) * [Nucleotide Formation: Biosynthesis and Assembly of DNA/RNA Building Blocks](/knowledge/molecular-biology/nucleotide-formation)