GO:0061863 microtubule plus end polymerase activity: Mechanism, Genes and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:0061863 microtubule plus end polymerase activity is a molecular function that catalyzes the reversible transfer of tubulin dimers to the plus end of a microtubule.
• The reaction is performed by TOG-domain array proteins such as XMAP215/ch-TOG, which use distinct structural features for polymerase activity versus plus-end tracking.
• Catalysis is thought to involve a template-based mechanism in which tubulin dimers are delivered processively to the growing plus end.
• Accessory factors including centriolar cap proteins CP110 and CPAP can restrict plus-end elongation, showing that polymerase activity is spatially and temporally controlled.
• The function is conserved from fungi to humans, with AlpA in Aspergillus nidulans guiding microtubule growth at the hyphal tip cortex.
• Dysregulation of microtubule plus-end dynamics is linked to cancer cell migration and other disease-relevant processes.
Description
Microtubule plus end polymerase activity (GO:0061863) is a molecular function that catalyzes the transfer of tubulin dimers to the plus end of a microtubule, a reaction that is reversible depending on the availability of dimers. This activity is distinct from simple tubulin binding because it directly promotes elongation of the microtubule polymer at its dynamic plus end. The function is essential for cellular processes that depend on controlled microtubule growth, including mitotic spindle assembly, cell migration, and polarity establishment. Researchers study this activity to understand how cells build and remodel their cytoskeleton with spatial and temporal precision. Because the reaction is reversible, the same catalytic site can in principle support both addition and removal of subunits, depending on the local concentration of tubulin dimers. This reversibility makes the polymerase a key node for regulating microtubule length and dynamics in response to cellular signals. The activity is carried out by proteins containing TOG-domain arrays, which are conserved across eukaryotes and are found in organisms ranging from fungi to humans. Structural and mechanistic studies have shown that the TOG arrays provide distinct surfaces for tubulin binding and for processive plus-end tracking, allowing the polymerase to remain associated with the growing end while it adds subunits. In this article, we summarize the definition, mechanism, key genes, disease relevance, and experimental approaches for studying GO:0061863, with a focus on how CRISPR-based models can be used to dissect its functions.
microtubule plus end polymerase activity At A Glance
| GO ID | GO:0061863 |
|---|---|
| GO term | microtubule plus end polymerase activity |
| Ontology | molecular_function |
| Synonym | none |
| Major function | Catalysis of the transfer of tubulin dimers to the plus end of a microtubule, with reversibility depending on dimer availability |
| Representative proteins | XMAP215/ch-TOG family TOG-domain array proteins, including ch-Tog and AlpA |
| Cellular context | Microtubule plus ends, mitotic spindle, cell cortex, and hyphal tip |
| Conservation | Found in eukaryotes from fungi to humans |
| Related activity | Microtubule plus-end tracking, which can be genetically separated from polymerase activity |
What Is GO:0061863?
GO:0061863 microtubule plus end polymerase activity is defined as the catalysis of the transfer of tubulin dimers to the plus end of a microtubule, where the reaction is reversible depending on the availability of dimers. In other words, it is an enzymatic activity that directly adds tubulin subunits to the growing plus end of a microtubule, rather than merely binding tubulin or regulating microtubule dynamics indirectly. The activity is typically associated with proteins that contain TOG-domain arrays and that can track the plus end while catalyzing elongation.
Why Is microtubule plus end polymerase activity Important in Cell Biology?
Microtubule plus end polymerase activity is important because it directly controls the rate and extent of microtubule elongation at the plus end, which in turn determines microtubule length, dynamics, and organization in cells. This activity is required for processes such as mitotic spindle assembly, cell migration, and the establishment of cell polarity, and its dysregulation has been linked to disease-relevant phenotypes including altered cell migration. Because the reaction is reversible, the polymerase can also contribute to microtubule depolymerization when dimer availability is low, making it a central regulator of microtubule turnover. Understanding this activity therefore provides insight into fundamental cytoskeletal mechanisms and offers potential targets for experimental intervention in cancer and other diseases.
• Controls the rate of microtubule plus-end elongation, a fundamental determinant of microtubule length and dynamics.
• Is required for mitotic spindle assembly and chromosome segregation, making it essential for cell division.
• Contributes to cell migration and polarity establishment, processes that are often dysregulated in cancer.
• Shows evolutionary conservation from fungi to humans, allowing mechanistic studies in model organisms.
• Can be separated genetically from plus-end tracking, enabling dissection of distinct protein functions.
• Is regulated by accessory factors such as CP110 and CPAP that restrict plus-end elongation.
• Provides a potential target for experimental modulation of microtubule dynamics in disease models.
• Is studied using structural, biochemical, and live-cell imaging approaches that reveal catalytic mechanisms.
What Happens During microtubule plus end polymerase activity?
Tubulin dimer delivery to the plus end
In simple terms: The polymerase grabs tubulin dimers and hands them to the growing end of the microtubule.
During microtubule plus end polymerase activity, tubulin dimers are transferred to the plus end of a microtubule in a reversible reaction. The polymerase must first bind tubulin dimers and then deliver them to the plus end, where they are incorporated into the polymer lattice. This step is distinct from simple tubulin sequestration because the dimer is directly added to the growing end. The reaction is reversible, so the same activity can support removal of subunits when dimer availability is low.
Processive plus-end tracking
In simple terms: The polymerase stays attached to the growing end while it adds subunits.
Many microtubule polymerases also track the plus end processively, meaning they remain associated with the growing tip while catalyzing elongation. Studies of TOG-domain arrays have shown that polymerase activity and processive plus-end tracking originate from distinct structural features within the arrays. This separation allows the protein to add subunits while maintaining contact with the plus end, which is important for efficient elongation.
Reversibility and dimer availability
In simple terms: If there are plenty of dimers, the polymerase adds them; if dimers are scarce, the reaction can go the other way.
The catalytic activity of microtubule polymerases is reversible and depends on the availability of tubulin dimers. When dimer concentration is high, the equilibrium favors addition of subunits to the plus end; when dimer concentration is low, the reaction can favor removal. This reversibility means that the polymerase can contribute to both microtubule growth and shrinkage depending on cellular conditions. Models for the catalytic activity of microtubule polymerases have been proposed to explain how this reversibility is achieved.
Regulation by accessory factors
In simple terms: Other proteins can put the brakes on the polymerase to control how fast microtubules grow.
Accessory factors can regulate microtubule plus end polymerase activity. For example, centriolar cap proteins CP110 and CPAP control slow elongation of microtubule plus ends, indicating that they can restrict polymerase-driven growth. In fungal hyphae, the cell-end marker TeaA and the microtubule polymerase AlpA contribute to microtubule guidance at the hyphal tip cortex, showing that polymerase activity is integrated with polarity machinery. These examples illustrate that the activity is not constitutive but is spatially and temporally controlled.
Key Genes Involved in GO:0061863 microtubule plus end polymerase activity
The following genes and proteins are experimentally implicated in microtubule plus end polymerase activity or its regulation, based on the verified literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| XMAP215/ch-TOG (human ch-TOG) | TOG-domain array protein with microtubule polymerase activity | Model for studying polymerase activity and plus-end tracking |
| AlpA (Aspergillus nidulans) | Microtubule polymerase involved in hyphal tip guidance | Fungal model for polarity maintenance and microtubule guidance |
| CP110 | Centriolar cap protein that controls slow elongation of microtubule plus ends | Regulator of plus-end elongation |
| CPAP | Centriolar cap protein that controls slow elongation of microtubule plus ends | Regulator of plus-end elongation |
| TeaA (Aspergillus nidulans) | Cell-end marker contributing to microtubule guidance at the hyphal tip cortex | Polarity maintenance model |
| EB1 | Microtubule plus-end tracking protein that interacts with regulators | Studied in cell migration and plus-end tracking |
| GTSE1 | Microtubule plus-end tracking protein that regulates EB1-dependent cell migration | Cancer cell migration model |
| TOG-domain array proteins (general) | Provide distinct features for polymerase activity and plus-end tracking | Structural and mechanistic studies |
| Microtubule end-binding proteins (general) | Structural and mechanistic insights into plus-end interactions | Comparative studies of end-binding mechanisms |
| Tubulin dimers | Substrate for the polymerase reaction | Biochemical assays of polymerase activity |
| MCAK (related) | Kinesin that regulates microtubule dynamics independently of ch-TOG | Comparison with polymerase functions |
| ch-Tog (XMAP215 family) | Microtubule plus-end dynamics factor with MCAK-independent functions | Dissection of polymerase versus depolymerase roles |
| CPAP (CENPJ) | Centriolar protein controlling plus-end elongation | Centriole and cilia research |
| CP110 (CCP110) | Centriolar cap protein controlling plus-end elongation | Centriole duplication and elongation studies |
| AlpA (homologs) | Fungal microtubule polymerase | Comparative evolution studies |
| TeaA (homologs) | Fungal cell-end marker | Polarity studies |
| EB1 (MAPRE1) | Plus-end tracking protein | Migration and cytoskeleton research |
| GTSE1 (human) | Plus-end tracking protein regulating EB1-dependent migration | Cancer migration models |
How Is microtubule plus end polymerase activity Regulated?
Microtubule plus end polymerase activity is regulated at multiple levels. Accessory proteins such as CP110 and CPAP can restrict plus-end elongation, thereby limiting polymerase-driven growth. In fungal hyphae, the cell-end marker TeaA and the polymerase AlpA cooperate to guide microtubules at the hyphal tip cortex, linking polymerase activity to polarity maintenance. The activity is also intrinsically regulated by the availability of tubulin dimers, because the reaction is reversible and depends on dimer concentration. Additionally, structural features within TOG-domain arrays determine whether a protein functions as a polymerase, a plus-end tracker, or both, providing a built-in regulatory mechanism. Post-translational modifications and interactions with other plus-end tracking proteins such as EB1 and GTSE1 may further modulate the activity in the context of cell migration.
microtubule plus end polymerase activity and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| GTSE1 | Cancer cell migration | Knockout in cancer cell lines followed by migration assays |
| CPAP (CENPJ) | Microcephaly and ciliopathies | Point-mutation knock-in in cell models |
| CP110 (CCP110) | Centriole elongation defects | Knockout and rescue with tagged knock-in |
| AlpA (Aspergillus nidulans) | Fungal polarity and growth | Gene deletion in fungal strains |
| ch-TOG (XMAP215) | Mitotic spindle defects | Knockout in human cell lines |
Cancer and cell migration
Microtubule plus end polymerase activity contributes to microtubule dynamics that underlie cell migration. GTSE1, a microtubule plus-end tracking protein, regulates EB1-dependent cell migration, and its dysregulation could affect migratory behavior of cancer cells. Because polymerase activity controls plus-end elongation, altered activity of TOG-domain proteins may influence invasion and metastasis, although direct evidence in human cancer is still emerging.
Centriole and cilia-related disorders
Centriolar cap proteins CP110 and CPAP control slow elongation of microtubule plus ends, and mutations in CPAP (CENPJ) are associated with microcephaly and other ciliopathies. Although the link to polymerase activity is indirect, the regulation of plus-end elongation by these proteins suggests that defects in this control could contribute to centriole-related diseases.
Fungal pathogenesis and polarity
In Aspergillus nidulans, the microtubule polymerase AlpA and the cell-end marker TeaA contribute to microtubule guidance at the hyphal tip cortex to provide polarity maintenance. Disruption of these factors could affect fungal growth and morphogenesis, which is relevant for understanding fungal infections, though direct human disease links are not established.
From microtubule plus end polymerase activity-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does loss of polymerase activity affect microtubule growth rate? | Knockout of TOG-domain gene in human cells |
| Can a point mutation separate polymerase activity from plus-end tracking? | Point-mutation knock-in of TOG-domain residues |
| How does tagging affect localization and function? | Tagged knock-in of endogenous polymerase |
| Does overexpression alter microtubule dynamics? | Overexpression of wild-type or mutant polymerase |
| What is the role of CP110/CPAP in plus-end elongation? | Knockout or knockdown of CP110/CPAP |
| How does AlpA contribute to hyphal polarity? | Gene deletion in Aspergillus nidulans |
How to Study the microtubule plus end polymerase activity Process
| Method | What It Measures | Typical Application |
|---|---|---|
| Live-cell imaging | Microtubule plus-end growth rate and dynamics | Quantifying polymerase activity in cells |
| TIRF microscopy with purified proteins | Direct catalysis of tubulin addition | In vitro reconstitution of polymerase activity |
| Structural biology (crystallography/cryo-EM) | TOG-domain array architecture | Mechanistic studies of tubulin transfer |
| Site-directed mutagenesis | Residues required for catalysis vs tracking | Dissecting distinct functions |
| CRISPR knockout | Loss-of-function effects on microtubule dynamics | Testing gene requirement |
| CRISPR knock-in of tags | Localization and interaction partners | Endogenous tagging for imaging |
| Fungal genetics | Polarity maintenance and microtubule guidance | Model organism studies |
| Migration assays | Cell migration dependent on plus-end tracking | Cancer cell biology |
Live-cell imaging of microtubule plus ends
Live-cell imaging with fluorescently labeled tubulin or plus-end tracking proteins is a primary method to measure microtubule plus end polymerase activity. By tracking the growth rate of individual microtubules, researchers can quantify the contribution of specific TOG-domain proteins to elongation. This approach has been used to show that ch-Tog functions in plus-end dynamics independently of MCAK.
In vitro reconstitution and TIRF microscopy
In vitro reconstitution of purified tubulin and recombinant polymerase domains allows direct measurement of catalytic activity using total internal reflection fluorescence (TIRF) microscopy. Such assays can reveal the reversibility of the reaction and the dependence on tubulin dimer concentration. They also help distinguish polymerase activity from plus-end tracking.
Structural biology and mutagenesis
Structural studies of TOG-domain arrays and microtubule end-binding proteins provide mechanistic insights into how tubulin dimers are transferred to the plus end. Site-directed mutagenesis combined with biochemical assays can identify residues required for catalysis versus tracking. These approaches have been used to propose models for the catalytic activity of microtubule polymerases.
Genetic analysis in model organisms
Fungal models such as Aspergillus nidulans allow genetic dissection of polymerase function in a polarized growth context. Deletion or mutation of AlpA and TeaA can reveal their roles in microtubule guidance at the hyphal tip cortex. Similar genetic approaches in human cells using CRISPR can test the function of XMAP215/ch-TOG and its regulators.
How CRISPR Can Be Used to Study GO:0061863 microtubule plus end polymerase activity
Knockout
CRISPR knockout of genes encoding microtubule polymerases or their regulators can reveal their requirement for microtubule plus end polymerase activity. For example, knocking out ch-TOG or XMAP215 family members in human cells allows assessment of plus-end dynamics and mitotic spindle assembly. Knockout of CP110 or CPAP can test their role in restricting plus-end elongation.
Point Mutation
Point mutations can be introduced into TOG-domain residues to separate polymerase activity from plus-end tracking. This approach is valuable because these functions originate from distinct structural features within TOG-domain arrays. Point-mutation knock-in of catalytic residues can also test models of the catalytic mechanism.
Knock-in
Knock-in of fluorescent or affinity tags at endogenous loci enables visualization and proteomic analysis of microtubule polymerases in their native context. Tagged knock-in of CP110 or CPAP can help track their localization at centrioles and their effects on plus-end elongation.
Overexpression
Overexpression of wild-type or mutant polymerases can test gain-of-function effects on microtubule dynamics. For example, overexpression of ch-TOG or its mutants can reveal dominant effects on plus-end growth. Overexpression of GTSE1 or EB1 can modulate cell migration in cancer models.
How EDITGENE Supports microtubule plus end polymerase activity Research
Researchers studying microtubule plus end polymerase activity-related genes often need to determine whether a candidate gene is causally involved in microtubule dynamics, cell migration, or disease phenotypes. This requires precise genetic models that can isolate the function of a single gene or mutation without confounding effects. EDITGENE provides a suite of CRISPR-based services designed to support such studies, from knockout to knock-in and library screening.
Contact EDITGENE today to design your custom CRISPR model for microtubule plus end polymerase activity research.
Frequently Asked Questions About microtubule plus end polymerase activity
What is microtubule plus end polymerase activity?
It is a molecular function (GO:0061863) that catalyzes the reversible transfer of tubulin dimers to the plus end of a microtubule.
What genes are involved in microtubule plus end polymerase activity?
Key genes include XMAP215/ch-TOG family members, AlpA in fungi, and regulators such as CP110 and CPAP.
How is microtubule plus end polymerase activity regulated?
It is regulated by tubulin dimer availability, accessory proteins like CP110 and CPAP, and structural features within TOG-domain arrays.
What is the difference between polymerase activity and plus-end tracking?
Polymerase activity catalyzes tubulin addition, while plus-end tracking is the ability to remain associated with the growing end; these functions originate from distinct features within TOG-domain arrays.
Which proteins have microtubule plus end polymerase activity?
Proteins containing TOG-domain arrays, such as XMAP215/ch-TOG and AlpA, exhibit this activity.
How can I study microtubule plus end polymerase activity in the lab?
Common methods include live-cell imaging, TIRF microscopy with purified proteins, structural biology, and CRISPR-based genetic models.
Is microtubule plus end polymerase activity reversible?
Yes, the reaction is reversible depending on the availability of tubulin dimers.
What diseases are linked to microtubule plus end polymerase activity?
Dysregulation has been linked to cancer cell migration and centriole-related disorders through proteins like GTSE1 and CPAP.
Can CRISPR be used to study microtubule plus end polymerase activity?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models are powerful tools for dissecting this activity.
What model organisms are used to study microtubule plus end polymerase activity?
Aspergillus nidulans is used to study AlpA and TeaA in hyphal polarity, while human cell lines are used for XMAP215/ch-TOG studies.
Conclusion
Microtubule plus end polymerase activity (GO:0061863) is a fundamental molecular function that catalyzes the reversible addition of tubulin dimers to the plus end of microtubules. It is carried out by conserved TOG-domain proteins and is regulated by accessory factors such as CP110 and CPAP. This activity is critical for mitotic spindle assembly, cell migration, and polarity maintenance, and its dysregulation is linked to cancer and centriole-related disorders. Studying this function requires a combination of live-cell imaging, in vitro reconstitution, structural biology, and CRISPR-based genetic models. EDITGENE provides comprehensive CRISPR services to support such research, from knockout to knock-in and library screening.
References
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- 3. Iyer SS et al.. 2025. Centriolar cap proteins CP110 and CPAP control slow elongation of microtubule plus ends.. J Cell Biol 224(3) PMID: 39847124
- 4. Xie P. 2023. A model for the catalytic activity of microtubule polymerases.. Cytoskeleton (Hoboken) 80(1-2):7-20 PMID: 36305831
- 5. Barr AR et al.. 2008. MCAK-independent functions of ch-Tog/XMAP215 in microtubule plus-end dynamics.. Mol Cell Biol 28(23):7199-211 PMID: 18809577
- 6. Slep KC. 2010. Structural and mechanistic insights into microtubule end-binding proteins.. Curr Opin Cell Biol 22(1):88-95 PMID: 19959349
- 7. Scolz M et al.. 2012. GTSE1 is a microtubule plus-end tracking protein that regulates EB1-dependent cell migration.. PLoS One 7(12):e51259 PMID: 23236459
- 8. Takeshita N et al.. 2013. The cell-end marker TeaA and the microtubule polymerase AlpA contribute to microtubule guidance at the hyphal tip cortex of Aspergillus nidulans to provide polarity maintenance.. J Cell Sci 126(Pt 23):5400-11 PMID: 24101725
