TACC/TOG complex

GO:0070850 · Cytoskeleton · Multiprotein complex · Proposed

A protein complex that contains the transforming acidic coiled coil (TACC) protein and the TOG protein (Mia1p/Alp7p and Alp14, respectively, in fission yeast), and is involved in microtubule array remodeling as cells progress through the cell cycle. The TACC/TOG complex is conserved in eukaryotes, associates with microtubules, and shuttles between the nucleus and the cytoplasm during interphase. [GO:0070850]

Reconstituted S. pombe Alp7/Alp14 activity. A diagrams the dual-TIRF assay; B-C show microtubule kymographs with Alp14-GFP alone or with Alp7, and D compares plus- and minus-end growth-rate distributions. The assay combines purified S. pombe proteins/tubulin with 2.5% labelled pig-brain tubulin and stabilized seeds. Kymograph bars are 2 micrometers and 1 minute. This is a functional reconstitution, not a resolved complex structure or whole-cell micrograph. FLUORESCENCE · *Schizosaccharomyces pombe* (`NCBITaxon:4896`) · Frauke Hussmann, Douglas R. Drummond, Daniel R. Peet, Douglas S. Martin, Robert A. Cross; Figure 7, DOI:10.1038/srep20653; CC BY 4.0, via PubMed Central. Original image unchanged; caption paraphrased. · CC_BY_4_0 · source: PMC PMC4749977.1 f7 · `DOI:10.1038/srep20653`

Synonyms: TACC-TOG complex; Alp7-Alp14 complex

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
TACC-family microtubule-associated protein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	alp7, mia1		UNKNOWN	Alp7 is the demonstrated fission-yeast TACC partner; it promotes Alp14 recruitment to organizing centers and carries the complex's nuclear import signal. `DOI:10.1038/srep20653` Purified full-length S. pombe Alp7 and Alp14 associate in sedimentation experiments; Alp14 binds soluble tubulin whereas Alp7 alone shows no detectable binding under the tested conditions. `DOI:10.1091/mbc.E13-11-0679` Alp7 provides the import signal; Alp14 L615A disrupts export while retaining Alp7 association. These transport results do not determine assembly essentiality. `DOI:10.1016/j.cub.2018.04.008` Alp7 deletion impairs Alp14 recruitment to MTOCs and efficient nucleation; persistent plus-end tracking distinguishes this recruitment contribution from an absolute requirement for elongation.
XMAP215	Protein	part of	`InterPro:IPR045110`	alp14, mtc1		UNKNOWN	Alp14 is the demonstrated fission-yeast TOG-family partner, tubulin-binding polymerase and carrier of the complex's nuclear export signal. `DOI:10.1038/srep20653` Purified full-length S. pombe Alp7 and Alp14 associate in sedimentation experiments; Alp14 binds soluble tubulin whereas Alp7 alone shows no detectable binding under the tested conditions. `DOI:10.1091/mbc.E13-11-0679` Alp7 provides the import signal; Alp14 L615A disrupts export while retaining Alp7 association. These transport results do not determine assembly essentiality.

Organism-specific protein examples

Named proteins in which each component's role was established, with the organism the evidence comes from. The component above is the taxon-agnostic family; these are the specific entries behind it.

TACC-family microtubule-associated protein

Accession	Protein	Gene	Organism	Entry
`UniProtKB:Q9URY2`	Microtubule protein alp7	alp7	Schizosaccharomyces pombe 972h- (`NCBITaxon:284812`)	REVIEWED
Role and evidence (2 references) Reference-sequence exemplar for species-level experiments, not an assertion that every experimental strain is this reference stock. `DOI:10.1038/srep20653` Purified full-length S. pombe Alp7 and Alp14 associate in sedimentation experiments; Alp14 binds soluble tubulin whereas Alp7 alone shows no detectable binding under the tested conditions. `https://www.uniprot.org/uniprotkb/Q9URY2/entry` Native accession, exact protein name, gene, reviewed status and source taxon verified on 2026-10-06; residence and binding are supported by the primary experiments.

XMAP215

Accession	Protein	Gene	Organism	Entry
`UniProtKB:O94534`	Spindle pole body component alp14	alp14	Schizosaccharomyces pombe 972h- (`NCBITaxon:284812`)	REVIEWED
Role and evidence (2 references) Reference-sequence exemplar for species-level experiments, not an assertion that every experimental strain is this reference stock. `DOI:10.1038/srep20653` Purified full-length S. pombe Alp7 and Alp14 associate in sedimentation experiments; Alp14 binds soluble tubulin whereas Alp7 alone shows no detectable binding under the tested conditions. `https://www.uniprot.org/uniprotkb/O94534/entry` Native accession, exact protein name, gene, reviewed status and source taxon verified on 2026-10-06; residence and binding are supported by the primary experiments.

Canonical examples

NCBITaxon:4896 Schizosaccharomyces pombe — Fission-yeast Alp7/Alp14 is the experimental exemplar. Purified-protein reconstitution and cellular perturbations do not establish prevalence across all fungi or microbial eukaryotes. [DOI:10.1038/srep20653]

Functions

microtubule plus end polymerase activity GO:0061863 — Alp14 mediates polymerase activity; Alp7 enhances tip occupancy in purified-protein assays. Alp7 dependence of cellular elongation differs between the 2016 and 2018 studies, so it is not treated as universally required.
- DOI:10.1038/srep20653 Purified S. pombe proteins and tubulin demonstrate plus-end growth regulation; Figure 7 uses a mixed-tubulin TIRF assay.
- DOI:10.1016/j.cub.2018.04.008 Alp7 deletion impairs nucleation while Alp14 still tracks tips and elongation rates remain normal in this study, unlike the earlier report.
microtubule nucleation GO:0007020 — The S. pombe complex supports efficient nucleation by recruiting Alp14 to organizing centers; loss-of-function and partial tethering rescue do not show that it is sufficient alone or required for every nucleation event.
- DOI:10.1016/j.cub.2018.04.008 Alp7 loss impairs Alp14 MTOC recruitment and nucleation. Forced Alp14 targeting to Mto1 partially rescues nucleation in the engineered assay.
mitotic spindle assembly GO:0090307 — Mitotic nuclear accumulation of Alp7/Alp14 supports spindle assembly in S. pombe closed mitosis.
- DOI:10.1091/mbc.E13-11-0679 Alp7 CDK-site mutations impair nuclear accumulation and spindle behavior; an added nuclear localization signal suppresses the growth defect, not proof of full spindle-phenotype rescue.
attachment of mitotic spindle microtubules to kinetochore GO:0051315 — Kinetochore-associated Alp7/Alp14 contributes to productive mitotic microtubule attachment in S. pombe.
- DOI:10.1091/mbc.E12-11-0817 Ndc80 loop mutation reduces kinetochore recruitment and compromises attachment. Forced Nuf2-Alp7 C-terminal targeting supports a recruitment contribution, without resolving the complete native interface.

Mechanism graphs

Purified Alp7-Alp14 association (ASSEMBLY)

S. pombe purified-protein association supports the binary partnership. This is not an ordered assembly pathway, a native subunit count, or a resolved interface.

Subject	Predicate	Object	Evidence
TACC-family microtubule-associated protein	binds	XMAP215	`DOI:10.1038/srep20653` Full-length proteins co-sediment as a complex; tubulin binding is attributable to Alp14 in the tested assay.

Recruitment, nucleation and attachment in fission yeast (FUNCTION)

S. pombe experiments separate MTOC recruitment/nucleation, plus-end polymerase activity and kinetochore attachment. Ndc80 and the nucleation-site machinery are external context, not extra TACC/TOG subunits.

Subject	Predicate	Object	Evidence
TACC-family microtubule-associated protein	supports recruitment of	Alp14 recruited to organizing centers	`DOI:10.1016/j.cub.2018.04.008` Localization, deletion and engineered Mto1-bonsai assays distinguish recruitment from elongation.
Alp14 recruited to organizing centers	promotes	microtubule nucleation	`DOI:10.1016/j.cub.2018.04.008` The engineered tether is a partial rescue, with expression and construct context limiting quantitative generalization.
TACC/TOG complex	supports	microtubule plus end polymerase activity	`DOI:10.1038/srep20653` Figure 7 uses S. pombe proteins/tubulin with labelled pig-brain tubulin and stabilized seeds; the claim is assay-specific. `DOI:10.1016/j.cub.2018.04.008` The 2018 cellular assays retain normal elongation and Alp14 tip tracking after Alp7 deletion. The authors explicitly contrast this with the earlier reduced-elongation result; the discrepancy remains unresolved.
Ndc80 kinetochore docking context	supports recruitment of	Kinetochore-associated Alp7/Alp14	`DOI:10.1091/mbc.E12-11-0817` Kinetochore signals decrease while spindle-pole localization is retained; full-complex geometry remains unresolved.
Kinetochore-associated Alp7/Alp14	supports	attachment of mitotic spindle microtubules to kinetochore	`DOI:10.1091/mbc.E12-11-0817` The forced fusion is a functional perturbation, not a native stoichiometric complex.

CDK-linked nuclear accumulation in closed mitosis (REGULATION)

S. pombe nuclear transport is distributed between the Alp7 import signal and Alp14 export signal. CDK-site evidence supports mitotic accumulation without proving a native importin-affinity mechanism or direct CDK inhibition of export.

Subject	Predicate	Object	Evidence
Mitotic CDK activity	promotes phosphorylation of	N-terminally phosphorylated Alp7	`DOI:10.1091/mbc.E13-11-0679` S50, S51, T100, T116 and T131 form the tested five-site alanine mutant; phosphorylation is reduced rather than necessarily eliminated.
N-terminally phosphorylated Alp7	promotes mitotic accumulation of	Nuclear Alp7/Alp14 accumulation	`DOI:10.1091/mbc.E13-11-0679` Leptomycin B permits delayed mutant nuclear accumulation; truncated-fragment two-hybrid results do not resolve full native importin binding.
TACC-family microtubule-associated protein	supports import of	Nuclear Alp7/Alp14 accumulation	`DOI:10.1091/mbc.E13-11-0679` Transport analysis separates the Alp7 NLS from mitotic accumulation control.
XMAP215	supports export toward	Cytoplasmic Alp7/Alp14 pool	`DOI:10.1091/mbc.E13-11-0679` Alp14 residues 601-620 confer export in a reporter; a direct resolved NES-Crm1 interface is not claimed.
Nuclear Alp7/Alp14 accumulation	supports	mitotic spindle assembly	`DOI:10.1091/mbc.E13-11-0679` CDK-site localization and spindle phenotypes provide functional evidence in fission-yeast closed mitosis.

Discussions

INTERPRETATION (RESOLVED): Keep the binary partnership distinct from the sites where it acts. GO:0070850 names a protein complex. MTOCs, microtubule ends, kinetochores and the nucleus are dynamic localization contexts, not universally asserted parent organelles.
CURATION_TODO (OPEN): Resolve an exact whole-protein grounding for the TACC component class. Q9URY2's complete native InterPro match result provides a fungal C-terminal domain and a coiled-coil entry, not an exact whole-protein family. This bounded search does not imply homolog absence.
KNOWLEDGE_GAP (OPEN): Determine native stoichiometry and assembly dependence separately from activity. Purified sedimentation supports association but not a universal native 2:2 copy count or interface geometry. Cellular growth, nucleation and transport defects do not independently measure whether the defined complex assembles without a constituent; essentiality remains UNKNOWN.
CONTROVERSY (OPEN): Reconcile the different effects of Alp7 loss on microtubule elongation. The 2016 study reports reduced elongation after Alp7 deletion and potentiation in reconstitution. The 2018 study finds normal elongation with persistent Alp14 tip tracking despite impaired nucleation, explicitly noting the discrepancy. Strain or assay conditions are possible explanations, not established resolutions.
INTERPRETATION (RESOLVED): Do not turn interaction partners and regulators into core subunits. Ndc80 supplies a kinetochore docking context; Mto1/gamma-tubulin machinery supplies nucleation sites; CDK and transport factors regulate localization. These experiments do not establish them as invariant constituents of the TACC/TOG binary partnership.
INTERPRETATION (RESOLVED): Do not infer a Dis1-containing TACC complex from shared family membership. Alp14 and Dis1 share XMAP215-family membership, but forced targeting at tested endogenous expression did not substitute their functions. Earlier overexpression cross-rescue prevents an absolute claim of nonexchangeability at every dose or in every lineage.
INTERPRETATION (RESOLVED): Separate the revised export assignment from unresolved transport mechanisms. Alp14 L615A retains Alp7 association whereas the older Alp7 L461A perturbation also breaks binding. Alp7 five-site phosphorylation mutants retain import. Truncated-fragment two-hybrid and reporter export data do not resolve native importin affinity or a NES-exportin interface.
KNOWLEDGE_GAP (OPEN): Extend direct microbial evidence beyond the fission-yeast exemplar. The GO definition describes eukaryotic conservation, but the curated mechanistic experiments here concern S. pombe. No clade-wide presence frequency, identical native stock, or universal transport mechanism is asserted.

Evidence

GO:0070850 Native OAK GO identity, definition and cellular-component namespace verified on 2026-10-06; direct is-a parent is GO:0140535 intracellular protein-containing complex. No universal organelle parthood is inferred from dynamic localization.
DOI:10.1038/srep20653 Purified full-length S. pombe Alp7 and Alp14 associate in sedimentation experiments; Alp14 binds soluble tubulin whereas Alp7 alone shows no detectable binding under the tested conditions.
DOI:10.1091/mbc.E13-11-0679 Full main Results, Discussion and Methods support the Alp7 import/Alp14 export division and CDK-linked mitotic localization; supplementary material was not read.
DOI:10.1016/j.cub.2018.04.008 Full main Results, Discussion and STAR Methods distinguish Alp7-dependent recruitment/nucleation from elongation and explicitly discuss the conflicting earlier elongation result; supplementary material was not read.
DOI:10.1091/mbc.E12-11-0817 Full main Results, Discussion and Methods support Ndc80-loop-dependent kinetochore association and attachment. Purified peptide binding is narrower than a resolved full-complex interface; supplementary material was not read.
DOI:10.3390/ijms20205108 Full main text, figure captions and strain table distinguish Alp14 and Dis1 under tested endogenous-expression and forced-targeting conditions, without claiming universal nonexchangeability at all doses.

Curation history

2026-10-06T04:52:04Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-06T04:57:30Z codex · EXPANDED_RECORD — Added verified parentage, two protein component classes, fission-yeast exemplar, four functions, three evidence-backed graphs, explicit experimental/model boundaries and eight discussions; imported the inspected unchanged CC BY 4.0 reconstitution figure.
2026-10-06T05:01:04Z codex · CORRECTED_EVIDENCE — Addressed issue 2090 by attaching the 2018 study directly to the TACC component recruitment role and the polymerase edge's contrasting elongation result; scientific claims, graph topology and PROPOSED status are unchanged.
2026-10-06T05:16:46Z codex · CORRECTED_ANCHORS — Addressed issue 2091 by replacing the native-assembly discussion's bare components anchor with the two existing component IDs; biological text, graph topology and embedding projection are unchanged.

Source: data/structures/cytoskeleton/tacc_tog_complex.yaml