tripartite attachment complex

GO:0120121 · Cytoskeleton · Other · Proposed

A three-part cytoskeletal structure in kinetoplastid species linking mitochondrial DNA organised in a kinetoplast through the mitochondrial membranes to the basal body. [GO:0120121]

Synonyms: TAC

Part of: GO:0005856 — cytoskeleton (no local record)

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

Components

Component	Type	Part of / acts on	Grounding	Genes	Essential	Role
unilateral filaments	Other	part of	Reviewed label only (reviewed name; no accession asserted)		UNKNOWN	Intramitochondrial filaments that connect the differentiated inner mitochondrial membrane to the flagellar face of the kDNA disk. `DOI:10.1091/mbc.E02-08-0525` Ogbadoyi, Robinson and Gull 2003, Results and Figures 2, 3 and 6: unilateral filaments occupy the intramitochondrial gap between the inner membrane and the kDNA disk, not the cytoplasmic basal-body side.
differentiated mitochondrial TAC membrane regions	Other	part of	Reviewed label only (reviewed name; no accession asserted)		UNKNOWN	Specialized mitochondrial outer- and inner-membrane regions crossed by the TAC as it links cytoplasmic exclusion-zone filaments to intramitochondrial unilateral filaments. `DOI:10.1091/mbc.E02-08-0525` Ogbadoyi, Robinson and Gull 2003 included differentiated mitochondrial membranes in the tripartite ultrastructure that spans the organellar envelope. `DOI:10.1073/pnas.1404854111` Schnarwiler et al. 2014 localized TAC40 to the outer mitochondrial membrane part of the TAC.
exclusion-zone filaments	Other	part of	Reviewed label only (reviewed name; no accession asserted)		UNKNOWN	Cytoplasmic filaments that link the proximal basal-body region to the differentiated outer mitochondrial membrane, occupying a zone depleted of cytoplasmic ribosomes. `DOI:10.1091/mbc.E02-08-0525` Ogbadoyi, Robinson and Gull 2003, Results and Figures 2, 3 and 6: exclusion-zone filaments connect basal bodies to the outer mitochondrial membrane, not the inner membrane to kDNA.
p166 TAC protein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)		UNKNOWN	T. brucei TAC protein that localizes between mitochondrial DNA and the flagellum and contributes to kDNA segregation. `DOI:10.1038/sj.emboj.7601956` Zhao et al. 2008 identified p166 as a link between the trypanosome mitochondrial DNA network and flagellum.
TAC40 mitochondrial outer-membrane beta-barrel protein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	TAC40	UNKNOWN	Mitochondrial outer-membrane beta-barrel protein positioned in the TAC membrane domain and required for mitochondrial genome inheritance in T. brucei. `DOI:10.1073/pnas.1404854111` Schnarwiler et al. 2014 characterized TAC40 as a TAC outer-mitochondrial-membrane beta-barrel protein.
TAC102 mitochondrial genome segregation protein	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	TAC102	UNKNOWN	TAC-localized protein in the mitochondrial matrix that is needed for normal TAC biogenesis and kDNA segregation. `DOI:10.1371/journal.ppat.1005586` Trikin et al. 2016 identified TAC102 as a TAC component of the T. brucei mitochondrial genome segregation machinery.

Taxonomic distribution

NCBITaxon:5691 Trypanosoma brucei — COMMON: The TAC has been imaged between the basal bodies and the kinetoplast in the single mitochondrion of T. brucei. [DOI:10.1091/mbc.E02-08-0525]

Canonical examples

NCBITaxon:5691 Trypanosoma brucei — Kinetoplastid model in which TAC102 was localized to the TAC and connected to normal TAC biogenesis and kDNA segregation by depletion experiments. [DOI:10.1371/journal.ppat.1005586]

Functions

basal-body-linked kinetoplast segregation — The TAC physically links the kinetoplast DNA disk to the flagellar basal bodies so that basal-body segregation helps position duplicated mitochondrial genomes.
- DOI:10.1091/mbc.E02-08-0525 Ogbadoyi, Robinson and Gull 2003 described a trans-membrane structural linkage responsible for mitochondrial genome positioning and segregation by flagellar basal bodies.
- DOI:10.1038/sj.emboj.7601956 Zhao et al. 2008 linked p166 depletion to kinetoplast missegregation.

Mechanism graphs

TAC domains bridge basal bodies to the kDNA disk (FUNCTION)

A nonmechanistic structural summary of the TAC bridge in T. brucei: basal bodies connect through cytoplasmic exclusion-zone filaments, differentiated mitochondrial membranes and intramitochondrial unilateral filaments to the kDNA disk. This is a spatial linkage, not a temporal assembly sequence or a resolved protein-by-protein force-transfer mechanism.

Subject	Predicate	Object	Evidence
ciliary basal body	aligns with	exclusion-zone filaments	`DOI:10.1091/mbc.E02-08-0525` Ogbadoyi, Robinson and Gull 2003, Results and Figures 2, 3 and 6 place exclusion-zone filaments on the basal-body-facing, cytoplasmic side of the TAC.
exclusion-zone filaments	connect through	differentiated mitochondrial TAC membrane regions	`DOI:10.1091/mbc.E02-08-0525` Ogbadoyi, Robinson and Gull 2003, Results and Figure 3 show exclusion-zone filaments terminating at the outer-membrane remnant after extraction.
differentiated mitochondrial TAC membrane regions	connect to	unilateral filaments	`DOI:10.1091/mbc.E02-08-0525` Ogbadoyi, Robinson and Gull 2003, Results and Figures 2, 3 and 6 place unilateral filaments between the inner membrane and the kDNA disk.
unilateral filaments	link to	kinetoplast DNA disk	`DOI:10.1091/mbc.E02-08-0525` Ogbadoyi, Robinson and Gull 2003, Results and Figures 2, 3 and 6 identify unilateral filaments as the intramitochondrial, kDNA-proximal arm of the TAC.
unilateral filaments	form	tripartite attachment complex	`DOI:10.1091/mbc.E02-08-0525` Ogbadoyi, Robinson and Gull 2003 defined the tripartite architecture of the basal-body-to-kDNA linkage.
tripartite attachment complex	mediates	basal-body-linked kinetoplast segregation	`DOI:10.1091/mbc.E02-08-0525` Ogbadoyi, Robinson and Gull 2003 connected the trans-membrane linkage to basal-body-driven mitochondrial genome segregation. `DOI:10.1371/journal.ppat.1005586` Trikin et al. 2016 characterized TAC102 as a TAC component in the mitochondrial genome segregation machinery.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral groundings for TAC structural domains and protein families. The first TAC record keeps the ultrastructural TAC domains and T. brucei TAC proteins label-only to avoid assigning broad or partial protein-family accessions as exact groundings.

Evidence

GO:0120121 Gene Ontology cellular-component term for the tripartite attachment complex.
DOI:10.1091/mbc.E02-08-0525 Ogbadoyi, Robinson and Gull 2003, A high-order trans-membrane structural linkage is responsible for mitochondrial genome positioning and segregation by flagellar basal bodies in trypanosomes, Molecular Biology of the Cell.
DOI:10.1038/sj.emboj.7601956 Zhao et al. 2008, p166, a link between the trypanosome mitochondrial DNA and flagellum, mediates genome segregation, EMBO Journal.
DOI:10.1073/pnas.1404854111 Schnarwiler et al. 2014, Trypanosomal TAC40 constitutes a novel subclass of mitochondrial beta-barrel proteins specialized in mitochondrial genome inheritance, PNAS.
DOI:10.1371/journal.ppat.1005586 Trikin et al. 2016, TAC102 Is a Novel Component of the Mitochondrial Genome Segregation Machinery in Trypanosomes, PLOS Pathogens.
GO:0005856 — cytoskeleton Gene Ontology lists GO:0120121 tripartite attachment complex as part_of cytoskeleton. This is parthood, not an is-a relation to the whole cytoskeletal framework.

Curation history

2026-09-13T09:41:13Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-13T09:41:59Z codex · EXPANDED_RECORD — Added TAC synonymy, cytoskeleton parentage, structural TAC-domain and TAC-protein components, Trypanosoma brucei scope, a kinetoplast-segregation function, core literature evidence, a nonmechanistic basal-body-to-kDNA bridge graph, and a grounding TODO.
2026-09-13T09:48:42Z codex · ADDRESS_REVIEW — #769: removed the unverified p166 gene_symbols value and narrowed the Trypanosoma brucei canonical example to the directly cited TAC102 study.
2026-10-12T04:59:13Z codex · ADDRESS_SAVED_REVIEW — Addressed issues 2284 and 2285: correct exclusion-zone versus unilateral filament compartments and the four bridge links from the defining primary paper; move cytoskeleton from is-a parentage to GO-supported parthood. Identity, protein claims, scientific status and earlier history are retained.

Source: data/structures/cytoskeleton/tripartite_attachment_complex.yaml