C1 axonemal microtubule

GO:1990719 · Cytoskeleton · Filament · Proposed

The asymmetric C1 singlet microtubule of the axonemal central pair. [GO:1990719]

Synonyms: C1 tubule

Part of: axonemal central pair (GO:0097540)

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

Taxonomic distribution

NCBITaxon:3055 Chlamydomonas reinhardtii — COMMON: Chlamydomonas flagellar central pair complexes contain an asymmetric C1 singlet microtubule with structurally distinct C1 projections. [DOI:10.1002/cm.21094]

Canonical examples

NCBITaxon:3055 Chlamydomonas reinhardtii — Green-algal model whose C1 microtubule and C1-associated central-pair projections were resolved by cryoelectron tomography and subtomogram averaging. [DOI:10.1002/cm.21094]

Functions

C1 projection scaffold — The C1 axonemal microtubule carries the structurally and biochemically distinct C1a, C1b, C1c, C1d, C1e and C1f central-pair projections.
- GO:1990719 GO distinguishes the C1 axonemal microtubule from C2 by the differing protein components of their projections.
- DOI:10.1002/cm.21094 Carbajal-Gonzalez et al. 2013 resolved the Chlamydomonas and Strongylocentrotus C1 microtubule projections, including newly assigned 1e and 1f densities.

Mechanism graphs

C1 axonemal microtubule carries C1 projections (FUNCTION)

In Chlamydomonas, the C1 singlet microtubule is one member of the axonemal central pair and carries C1-specific projections while the central bridge links it to C2.

Subject	Predicate	Object	Evidence
C1 axonemal microtubule	is part of	axonemal central pair	`GO:1990719` GO places the C1 axonemal microtubule within the axonemal central pair.
C1 central-pair projections	project from	C1 axonemal microtubule	`DOI:10.1002/cm.21094` Carbajal-Gonzalez et al. 2013 resolved C1a, C1b, C1c, C1d, C1e and C1f projection densities on the C1 microtubule.
axonemal central bridge	connects to	C1 axonemal microtubule	`GO:1990717` GO defines the axonemal central bridge as connecting the central pair of single microtubules.
axonemal central bridge	connects to	C2 axonemal microtubule	`GO:1990717` GO defines the axonemal central bridge as two bridges linking the two central-pair microtubules.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral boundaries, C1 microtubule-wall constituents, protein-family groundings and copy numbers for the C1 axonemal microtubule and C1a/C1b/C1c/C1d/C1e/C1f projection subcomplexes. Carbajal-Gonzalez et al. 2013 resolved six named C1 projection densities, but this pass curates only the broad GO:1990719 C1 axonemal microtubule scaffold and leaves its exact tubulin wall constituents and C1 projection subcomplex boundaries unresolved.

Evidence

GO:1990719 Gene Ontology cellular-component term for the C1 axonemal microtubule.
GO:0005879 Gene Ontology places the C1 axonemal microtubule under the axonemal microtubule class.
GO:0097540 Gene Ontology places the C1 axonemal microtubule within the axonemal central pair.
DOI:10.1002/cm.21094 Carbajal-Gonzalez et al. 2013, 'Conserved structural motifs in the central pair complex of eukaryotic flagella', Cytoskeleton.

Curation history

2026-09-23T16:15:56Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-23T16:16:58Z codex · EXPANDED_RECORD — Added the C1 tubule synonym, axonemal-microtubule parentage, central-pair parthood, Chlamydomonas scope, GO and DOI evidence, a nonmechanistic C1 projection graph, and a C1 projection subcomplex TODO.
2026-09-23T16:27:02Z codex · ADDRESSED_REVIEW — Resolved PR #1408 review issue #1409 by keeping exact C1 microtubule-wall constituents in the C1 projection graph scope note and TODO.

Source: data/structures/cytoskeleton/c1_axonemal_microtubule.yaml