nucleus-basal body connector

cellstructuremech:nucleus_basal_body_connector · Cytoskeleton · Other · Proposed

A centrin-containing fibrous root system that links flagellar basal bodies to the nuclear surface. It is a specialized nucleus-associated rootlet system, not the entire basal apparatus or the fibers connecting basal bodies to one another. [DOI:10.1083/jcb.101.5.1903]

Image (not hosted — CC_BY_NC_SA_4_0): PMC2114663.1 Figure 2

Figure 2: phase-contrast cells, DAPI-stained nuclei and immunolabeled roots before shock, after shock and during recovery. Source scale bar: 5 micrometers. FLUORESCENCE · Chlamydomonas reinhardtii (NCBITaxon:3055) · J. L. Salisbury, M. A. Sanders and L. Harpst, Figure 2, Journal of Cell Biology 105 (1987), doi:10.1083/jcb.105.4.1799, via PubMed Central; CC BY-NC-SA 4.0. Link only; no repository copy or adaptation. · CC_BY_NC_SA_4_0 · source: PMC PMC2114663.1 Figure 2 · DOI:10.1083/jcb.105.4.1799

Synonyms: NBBC; nucleo-basal body connector; basal body-nucleus connector; rhizoplast; system II fiber

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
Nucleus-basal body connector centrins	Protein	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Centrin-family calcium-binding constituents of the connector fibers; normal assembly depends on centrin function in the tested Chlamydomonas mutants. `DOI:10.1083/jcb.101.5.1903` Connector immunoreactivity and biochemical identification of an acidic approximately 20-kDa protein. `DOI:10.1083/jcb.119.6.1613` E101K centrin and intragenic revertants distinguish normal connector formation from other centrin-containing assemblies. `DOI:10.1007/s00709-003-0016-4` Primary abstract reports centrin immunoreactivity and Synura cytoskeleton immunoblots; no sequence-level identity for these examples is assigned.

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.

Nucleus-basal body connector centrins

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P05434`	Caltractin		Chlamydomonas reinhardtii (`NCBITaxon:3055`)	REVIEWED
Role and evidence (2 references) Species-level centrin example, not a connector-specific paralogue or a complete connector inventory. `UniProtKB:P05434` Verified reviewed entry, recommended name, organism and sequence-source citations; no primary gene symbol is supplied by the entry. `DOI:10.1083/jcb.119.6.1613` Centrin/caltractin sequence and vfl2 linkage establish the tested protein; mutant and revertant analysis includes connector assembly. Methods use the cloned centrin sequence cited by the UniProt entry.

Canonical examples

NCBITaxon:3055 Chlamydomonas reinhardtii — The contraction experiments used gametes of a 137c derivative; no culture-collection strain accession is inferred. [DOI:10.1083/jcb.105.4.1799]
NCBITaxon:52555 Synura petersenii — Primary abstract describes a centrin-containing rootlet claw between basal bodies and nucleus, including mitotic observations. [DOI:10.1007/s00709-003-0016-4]
NCBITaxon:420600 Mallomonas insignis — Included in the primary abstract's ultrastructural comparison of nucleus-associated rhizoplasts; contraction is not demonstrated here. [DOI:10.1007/s00709-003-0016-4]

Functions

nucleus localization GO:0051647 — Connector shortening and reextension reposition the nucleus relative to the basal apparatus in Chlamydomonas.
- DOI:10.1083/jcb.101.5.1903 Calcium shortens connectors in isolated nucleo-flagellar preparations.
- DOI:10.1083/jcb.105.4.1799 Living gametes and extracted models show coupled changes in root configuration and nuclear position.

Mechanism graphs

Calcium-driven connector movement and ATP potentiation in extracted Chlamydomonas models (FUNCTION)

Assay-level contractile mechanism, not an atomic motor model. The calcium step requires a responsive preparation; prior ATP treatment restores responsiveness after a refractory cycle.

Subject	Predicate	Object	Evidence
Elevated free calcium in assay buffer	triggers	Connector contraction	`DOI:10.1083/jcb.105.4.1799` Results and Table I; a refractory preparation does not respond without potentiation.
Connector contraction	draws the nucleus toward the basal apparatus	Anterior nuclear displacement	`DOI:10.1083/jcb.105.4.1799` Figure 2 and extracted-model experiments.
Calcium chelation by EGTA	permits	Connector reextension	`DOI:10.1083/jcb.105.4.1799` Results and Table I.
Connector reextension	accompanies return of	Return toward central nuclear position	`DOI:10.1083/jcb.105.4.1799` Extracted-model reactivation results; no separate nuclear motor is assigned.
ATP treatment of refractory models	restores	Restored calcium responsiveness	`DOI:10.1083/jcb.105.4.1799` Table I tests ATP before or during renewed calcium exposure.
Restored calcium responsiveness	permits renewed calcium-triggered	Connector contraction	`DOI:10.1083/jcb.105.4.1799` Sequential treatment conditions in Table I.

Discussions

CURATION_TODO (RESOLVED): Separate the named connector from other basal-apparatus fibers. Shared centrin or historical rootlet terminology does not establish equivalent structure identities.
CURATION_TODO (OPEN): Resolve exact connector-centrin family grounding and the remaining scaffold composition. A verified protein example does not define a cross-taxon family or a full molecular inventory.
CURATION_TODO (OPEN): Resolve connector-specific contributions to basal-body segregation independently of other centrin structures. The vfl2 mutation affects several assemblies, so its entire phenotype cannot be assigned to the connector alone.
CURATION_TODO (OPEN): Determine the molecular basis of ATP potentiation and native force generation. Reactivation experiments establish conditional responses, not every biochemical intermediate.
CURATION_TODO (RESOLVED): Do not assert that connector contraction is required for flagellar gene induction. An early signaling hypothesis has later negative evidence.
CURATION_TODO (OPEN): Compare connector variants and verify source details beyond the demonstrated examples. Similar topology does not prove universal distribution, identical dynamics or molecular homology across every rhizoplast.

Evidence

DOI:10.1083/jcb.101.5.1903 Primary identity, isolation and localization study; inspected PDF text on pages 1, 2, 8 and 9.
DOI:10.1083/jcb.105.4.1799 Full seven-page primary PDF read; Figure 2 and Table I visually inspected.
DOI:10.1002/cm.970140409 Primary abstract read through Europe PMC; full experimental text not read. Includes negative gene-induction evidence.
DOI:10.1083/jcb.119.6.1613 Primary sequence, mutant/revertant and ultrastructural evidence; Methods, Results and Table II inspected.
DOI:10.1007/s00709-003-0016-4 Primary abstract read. Full experimental text and figures not read; species comparisons remain abstract-bounded.
DOI:10.1128/EC.4.7.1253-1263.2005 Verified primary abstract and partial indexed text describe a larger centrin scaffold. Not treated as a fully inspected paper or proof of specific connector-binding proteins.
GO:0035253 Verified ciliary rootlet term; broad is-a parent, not exact connector identity.
GO:0051647 Verified nucleus localization term for the observed positional changes.

Curation history

2026-10-04T03:40:50Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-04T03:43:01Z codex · EXPANDED_RECORD — Added source-bounded connector identity, centrin component and verified protein example, three canonical taxa, nuclear-localization function, conditional contraction graph, link-only figure and explicit evidence limitations.

Source: data/structures/cytoskeleton/nucleus_basal_body_connector.yaml