GO:0140708 CAT tailing: Ribosome Quality Control Pathway, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• CAT tailing (GO:0140708) is the C-terminal elongation of 60S-anchored stalled nascent polypeptide chains with untemplated alanine and threonine tails.
• CAT tails are added by the ribosome-associated quality control (RQC) factor NEMF and are recognized by the RQC system to target stalled nascent chains for degradation.
• The process is eIF5A-dependent and occurs on 60S ribosomal subunits that remain after ribosome splitting.
• CAT tailing acts as a fail-safe mechanism to ensure efficient degradation of stalled nascent polypeptides.
• Vms1 antagonizes CAT tailing to protect mitochondria from toxic CAT-tailed proteins.
• Dysregulation of CAT tailing is linked to neurodegeneration and mitochondrial dysfunction.
Description
CAT tailing (GO:0140708) is a biological process that modifies stalled nascent polypeptide chains on 60S ribosomal subunits by adding untemplated alanine and threonine tails. This modification is a key step in ribosome-associated quality control (RQC), a surveillance pathway that detects and eliminates aberrant translation products. The addition of CAT tails marks the stalled nascent chain for recognition by the RQC machinery, leading to its ubiquitination and proteasomal degradation. Understanding CAT tailing is crucial because it represents a fundamental cellular strategy to maintain proteostasis and prevent the accumulation of toxic protein aggregates. Research has shown that CAT tailing is conserved in eukaryotes and involves specialized factors such as NEMF and eIF5A. Defects in this process have been implicated in mitochondrial dysfunction and neurodegenerative diseases, making it a topic of intense investigation. This article provides a comprehensive overview of CAT tailing, covering its definition, mechanism, key genes, disease relevance, and research methodologies.
CAT tailing At A Glance
| GO ID | GO:0140708 |
|---|---|
| GO term | CAT tailing |
| Ontology | biological_process |
| Synonym | None |
| Major function | C-terminal elongation of stalled nascent chains with alanine and threonine tails for quality control recognition |
| Cellular location | Cytosol, on 60S ribosomal subunits |
| Key enzymes | NEMF (Rqc2), eIF5A |
| Substrates | Stalled nascent polypeptide chains |
| Related pathway | Ribosome-associated quality control (RQC) |
What Is GO:0140708?
CAT tailing is the C-terminal elongation of 60S-anchored stalled nascent polypeptide chains with untemplated alanine and threonine tails (CAT tails). These tails participate in the recognition of stalled nascent chains by the ribosome quality control system, leading to their degradation.
Why Is CAT tailing Important in Cell Biology?
CAT tailing is essential for cellular proteostasis because it ensures that stalled translation products are efficiently targeted for degradation, preventing the accumulation of potentially toxic proteins. This process is particularly important in neurons and mitochondria, where protein quality control is critical for function and survival. Dysregulation of CAT tailing has been linked to neurodegenerative diseases and mitochondrial dysfunction, highlighting its physiological significance. Moreover, CAT tailing is a conserved mechanism that provides insights into fundamental aspects of translation and protein quality control.
• Prevents accumulation of toxic stalled nascent polypeptides by marking them for degradation.
• Acts as a fail-safe mechanism in ribosome-associated quality control (RQC).
• Protects mitochondria from toxic CAT-tailed proteins through Vms1-mediated antagonism.
• Implicated in neurodegeneration when dysregulated.
• Requires eIF5A for efficient CAT tailing, linking to translation elongation factors.
• Involved in translocation-associated quality control at the endoplasmic reticulum.
• Provides a model for studying ribosome stalling and rescue.
• Potential target for therapeutic intervention in diseases of protein misfolding.
• Conserved from yeast to humans, facilitating genetic studies.
• Crosstalk with other quality control pathways such as the unfolded protein response.
What Happens During CAT tailing?
Recognition of Stalled Ribosomes
In simple terms: When a ribosome gets stuck while making a protein, the cell needs to recognize it and start a rescue process.
CAT tailing begins with the recognition of a stalled 80S ribosome, which is then split into 60S and 40S subunits by the RQC machinery. The 60S subunit remains bound to the incomplete nascent polypeptide chain and is targeted by RQC factors. This recognition step is crucial for initiating the downstream events of CAT tailing.
Recruitment of NEMF and eIF5A
In simple terms: Special proteins called NEMF and eIF5A are recruited to the stalled ribosome to add the CAT tail.
The RQC factor NEMF (also known as Rqc2 in yeast) binds to the 60S subunit and recruits the translation elongation factor eIF5A. eIF5A is required for the addition of alanine and threonine residues to the C-terminus of the stalled nascent chain. This recruitment is a key step in CAT tailing and is regulated by the availability of these factors.
Synthesis of the CAT Tail
In simple terms: The CAT tail is built by adding alanine and threonine amino acids one by one to the end of the stuck protein.
NEMF, together with eIF5A, catalyzes the untemplated addition of alanine and threonine residues to the C-terminus of the nascent chain, forming the CAT tail. This elongation does not require a messenger RNA template and occurs on the 60S subunit. The length and composition of the CAT tail can vary and are thought to influence the fate of the nascent chain.
Recognition and Ubiquitination
In simple terms: The CAT tail acts like a tag that tells the cell to destroy the faulty protein.
The CAT tail is recognized by the RQC system, which then ubiquitinates the nascent chain. This ubiquitination targets the stalled polypeptide for proteasomal degradation. The CAT tail is essential for efficient recognition and degradation, as without it, stalled chains may accumulate.
Degradation of the Nascent Chain
In simple terms: The tagged protein is chopped up by the proteasome, a cellular recycling machine.
Following ubiquitination, the CAT-tailed nascent chain is extracted from the 60S subunit and degraded by the proteasome. This step requires the Cdc48/p97 ATPase complex in some contexts. The degradation of the stalled chain prevents the accumulation of potentially toxic protein aggregates.
Antagonism by Vms1
In simple terms: A protein called Vms1 can stop CAT tailing to protect mitochondria from damage.
Vms1 (also known as ANKZF1 in humans) is a cytosolic protein that antagonizes CAT tailing by removing the CAT tail or preventing its addition. This activity is important for protecting mitochondria from toxic CAT-tailed proteins that can mislocalize and impair mitochondrial function. Vms1 thus provides a regulatory counterbalance to CAT tailing.
Key Genes Involved in GO:0140708 CAT tailing
The following genes and proteins are central to CAT tailing and its regulation, as identified in the literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| NEMF (Rqc2) | Catalyzes addition of alanine and threonine to stalled nascent chains | Core enzyme of CAT tailing; knockout leads to loss of CAT tails |
| eIF5A | Translation elongation factor required for CAT tailing | Essential for CAT tailing; knockdown inhibits tail synthesis |
| Vms1 (ANKZF1) | Antagonizes CAT tailing; protects mitochondria | Regulator of CAT tailing; overexpression reduces toxic CAT-tailed proteins |
| Rqc1 | Component of RQC complex; involved in recognition of CAT tails | Required for ubiquitination of stalled chains |
| Rqc2 | Yeast ortholog of NEMF; adds CAT tails | Model for studying CAT tailing in yeast |
| Ltn1 | E3 ubiquitin ligase that ubiquitinates stalled chains | Works downstream of CAT tailing |
| Cdc48/p97 | AAA-ATPase that extracts stalled chains from 60S | Required for degradation of CAT-tailed proteins |
| Ribosome | 60S subunit serves as platform for CAT tailing | Structural studies reveal binding sites |
| tRNA-Ala | Provides alanine for CAT tail | Substrate for NEMF-mediated elongation |
| tRNA-Thr | Provides threonine for CAT tail | Substrate for NEMF-mediated elongation |
| Hbs1 | Recognizes stalled ribosomes and recruits RQC | Upstream of CAT tailing |
| Dom34 | Splits stalled ribosomes | Upstream of CAT tailing |
| ZNF598 | Ubiquitinates 40S proteins upon stalling | Initiates RQC |
| GCN1 | Activates GCN2 in response to stalling | Links CAT tailing to stress response |
| RACK1 | Ribosome-associated protein involved in quality control | Modulates CAT tailing efficiency |
| eRF1 | Termination factor; may be involved in stalling | Context-dependent |
How Is CAT tailing Regulated?
CAT tailing is regulated at multiple levels. The availability of eIF5A and NEMF is critical, as their depletion reduces CAT tailing efficiency. Vms1 acts as a direct antagonist, limiting CAT tailing to protect mitochondria. Additionally, the mechanochemical forces within the ribosome tunnel can influence the composition and fate of stalled nascent chains, thereby affecting CAT tailing. The process is also linked to the integrated stress response, as stalled ribosomes can activate GCN2, which may feedback on CAT tailing.
CAT tailing and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| Vms1 (ANKZF1) | Neurodegeneration, mitochondrial dysfunction | Knockout mice or neuronal cell lines |
| NEMF | Cancer, proteostasis disorders | Knockout cell lines, xenografts |
| eIF5A | Cancer, neurodegeneration | Point mutation (K50A) knock-in cells |
| Rqc1 | Not directly linked to disease | Yeast models |
| Ltn1 | Neurodegeneration | Knockout mice |
Neurodegeneration
Dysregulation of CAT tailing has been implicated in neurodegenerative diseases. Vms1, a CAT tailing antagonist, is important for neuronal survival, and its loss leads to mitochondrial dysfunction and neurodegeneration in models. Accumulation of CAT-tailed proteins may contribute to proteotoxicity in neurons.
Mitochondrial Dysfunction
CAT-tailed proteins can mislocalize to mitochondria and impair their function. Vms1 protects mitochondria by antagonizing CAT tailing, and its deficiency exacerbates mitochondrial damage. This link suggests that CAT tailing is relevant to mitochondrial diseases.
Cancer
Alterations in RQC components, including NEMF and eIF5A, have been observed in various cancers, though the specific role of CAT tailing in cancer remains to be fully elucidated. eIF5A is known to be involved in cell proliferation and is a potential therapeutic target.
From CAT tailing-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| What is the role of NEMF in CAT tailing? | NEMF knockout cell lines |
| How does eIF5A contribute to CAT tailing? | eIF5A knockdown or point mutant (K50A) |
| Does Vms1 protect against CAT-tailed protein toxicity? | Vms1 overexpression or knockout |
| What is the fate of CAT-tailed proteins? | Tagged knock-in of NEMF or nascent chain reporters |
| How does CAT tailing affect translation? | Ribo-seq in knockout cells |
| Can CAT tailing be visualized in live cells? | Fluorescent tagging of NEMF and nascent chains |
How to Study the CAT tailing Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Ribo-seq | Ribosome occupancy and stalling | Identify CAT tailing substrates |
| Mass spectrometry | Protein identity and modifications | Characterize CAT-tailed proteins |
| Fluorescence microscopy | Localization and dynamics of CAT tailing factors | Live-cell imaging |
| CRISPR screening | Genes affecting CAT tailing | Discover regulators |
| Western blot | Protein levels and ubiquitination | Assess degradation of stalled chains |
| Polysome profiling | Ribosome subunit distribution | Detect 60S-bound nascent chains |
| In vitro translation | CAT tailing activity | Reconstitute with purified components |
| Yeast genetics | Genetic interactions | Identify conserved factors |
Ribosome Profiling (Ribo-seq)
Ribo-seq allows genome-wide mapping of ribosome positions and can detect stalled ribosomes that are substrates for CAT tailing. By comparing wild-type and mutant cells, researchers can identify changes in ribosome stalling and CAT tailing efficiency.
Proteomics and Mass Spectrometry
Mass spectrometry can identify CAT-tailed proteins and characterize the composition of the CAT tail. This method is useful for understanding which proteins are targeted for CAT tailing under different conditions.
Fluorescence Microscopy
Fluorescent tagging of NEMF, eIF5A, and nascent chains enables visualization of CAT tailing in live cells. This approach provides spatial and temporal information about the process.
CRISPR Screening
Genome-wide CRISPR screens can identify genes that regulate CAT tailing or are required for the degradation of CAT-tailed proteins. Such screens have revealed novel components of the RQC pathway.
How CRISPR Can Be Used to Study GO:0140708 CAT tailing
Knockout
CRISPR knockout of NEMF or eIF5A abolishes CAT tailing, leading to accumulation of stalled nascent chains. These models are used to study the consequences of CAT tailing loss on proteostasis and cell viability.
Point Mutation
Point mutations in eIF5A (e.g., K50A) that impair its function can be introduced to dissect its specific role in CAT tailing. Such models help distinguish between eIF5A's general translation roles and its function in CAT tailing.
Knock-in
Knock-in of tagged NEMF or eIF5A allows for affinity purification and imaging of CAT tailing complexes. This approach enables the study of dynamic interactions during CAT tailing.
Overexpression
Overexpression of Vms1 or its human ortholog ANKZF1 can suppress CAT tailing and protect against toxicity. Overexpression models are useful for testing therapeutic strategies.
How EDITGENE Supports CAT tailing Research
Researchers studying CAT tailing-related genes often need to determine whether a candidate gene is causally involved in the process or in associated diseases. EDITGENE provides a comprehensive suite of CRISPR services to facilitate such investigations, from gene knockout to precise point mutations and knock-in of reporters.
Contact EDITGENE today to design your custom CRISPR model for CAT tailing research.
Frequently Asked Questions About CAT tailing
What is CAT tailing?
CAT tailing is the addition of untemplated alanine and threonine tails to stalled nascent polypeptide chains on 60S ribosomal subunits, marking them for degradation.
What genes are involved in CAT tailing?
Key genes include NEMF (Rqc2), eIF5A, Vms1 (ANKZF1), Rqc1, Ltn1, and Cdc48/p97.
What is the function of CAT tails?
CAT tails are recognized by the ribosome quality control system to target stalled nascent chains for ubiquitination and proteasomal degradation.
How is CAT tailing regulated?
CAT tailing is regulated by the availability of NEMF and eIF5A, and antagonized by Vms1 to protect mitochondria.
What diseases are associated with CAT tailing?
Dysregulation of CAT tailing has been linked to neurodegeneration and mitochondrial dysfunction.
Which enzyme adds CAT tails?
NEMF (Rqc2 in yeast) is the enzyme that adds alanine and threonine residues to stalled nascent chains.
Is CAT tailing conserved?
Yes, CAT tailing is conserved from yeast to humans.
What is the role of eIF5A in CAT tailing?
eIF5A is a translation elongation factor required for the addition of CAT tails.
How does Vms1 affect CAT tailing?
Vms1 antagonizes CAT tailing by removing or preventing the addition of CAT tails, protecting mitochondria.
What methods are used to study CAT tailing?
Common methods include Ribo-seq, mass spectrometry, fluorescence microscopy, and CRISPR screening.
Conclusion
CAT tailing (GO:0140708) is a critical biological process that ensures the degradation of stalled nascent polypeptides through the addition of alanine and threonine tails. Its regulation by NEMF, eIF5A, and Vms1 highlights its importance in proteostasis and mitochondrial health. Dysregulation of CAT tailing is implicated in neurodegeneration and mitochondrial diseases, making it a promising target for therapeutic intervention. Continued research using advanced CRISPR models and omics technologies will further elucidate its mechanisms and disease relevance.
References
- 1. Howard CJ et al.. 2021. Ribosome-associated quality control and CAT tailing.. Crit Rev Biochem Mol Biol 56(6):603-620 PMID: 34233554
- 2. Ennis A et al.. 2025. NEMF-mediated CAT tailing facilitates translocation-associated quality control.. J Cell Biol 224(6) PMID: 40257401
- 3. Ennis A et al.. 2024. NEMF-mediated CAT-tailing defines distinct branches of translocation-associated quality control.. bioRxiv PMID: 39253483
- 4. Tesina P et al.. 2023. Molecular basis of eIF5A-dependent CAT tailing in eukaryotic ribosome-associated quality control.. Mol Cell 83(4):607-621.e4 PMID: 36804914
- 5. Kostova KK et al.. 2017. CAT-tailing as a fail-safe mechanism for efficient degradation of stalled nascent polypeptides.. Science 357(6349):414-417 PMID: 28751611
- 6. Kreft SG et al.. 2018. Vms1: A Cytosolic CAT-Tailing Antagonist to Protect Mitochondria.. Trends Cell Biol 28(1):3-5 PMID: 29203248
- 7. Khan D et al.. 2024. Mechanochemical forces regulate the composition and fate of stalled nascent chains.. bioRxiv PMID: 39131335
- 8. Bertram N et al.. 2025. Delayed protein translocation protects mitochondria against toxic CAT-tailed proteins.. Mol Cell 85(21):4082-4092.e7 PMID: 41118763
