polarisome

GO:0000133 · Other · Multiprotein complex · Proposed

A fungal cell-polarity protein complex that localizes to sites of polarized growth and directs localized actin-filament assembly, including the Saccharomyces Bni1/Spa2/Pea2/Bud6 polarisome. [GO:0000133]

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
Spa2/Pea2 polarisome scaffold	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	SPA2, PEA2	CONDITIONAL	Core scaffold proteins that localize to polarized-growth sites and help organize the Saccharomyces polarisome. `DOI:10.1083/jcb.135.3.725` Valtz and Herskowitz 1996 showed that Pea2 localizes to polarized-growth sites in a pattern similar to Spa2 and that Pea2 and Spa2 depend on one another for stable localization. `DOI:10.1083/jcb.202006193` Dunkler et al. 2021 studied Spa2 and Pea2 as known polarisome proteins recruited by type V myosin in budding yeast.
Bni1 formin	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	BNI1	CONDITIONAL	Formin effector that nucleates actin filament assembly from the budding-yeast polarisome. `GO:0000133` GO:0000133 lists Bni1p among Saccharomyces polarisome proteins. `DOI:10.1128/MCB.18.7.4053` Sheu et al. 1998 connected Spa2 with Bni1 and other yeast morphogenesis proteins. `DOI:10.1038/s41467-019-13125-1` Xie et al. 2019 modeled Aip5, Bni1, and Bud6 around Spa2-mediated actin polymerization.
Bud6 actin nucleation-promoting factor	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	BUD6, AIP3	CONDITIONAL	Actin nucleation-promoting factor associated with the Bni1-containing budding-yeast polarisome. `GO:0000133` GO:0000133 lists Bud6p among Saccharomyces polarisome proteins. `DOI:10.1038/s41467-019-13125-1` Xie et al. 2019 studied Bud6 with Bni1 in a Spa2-mediated actin-polymerization system.

Taxonomic distribution

NCBITaxon:4751 Fungi — VARIABLE: Polarisome proteins and tip-localized polarisome-like assemblies are characterized in budding yeasts and filamentous fungi, but the exact component arrangement varies with growth mode and lineage. [DOI:10.1371/journal.pone.0030372]

Canonical examples

NCBITaxon:4932 Saccharomyces cerevisiae — Budding-yeast model in which Pea2 and Spa2 localize to polarized-growth sites during budding and mating. [DOI:10.1083/jcb.135.3.725]
NCBITaxon:5141 Neurospora crassa — Filamentous fungal model in which SPA-2, BUD-6, and BNI-1 have distinct localizations around the apical dome and Spitzenkorper during hyphal growth. [DOI:10.1371/journal.pone.0030372]

Functions

polarized actin assembly — The polarisome scaffolds actin-assembly factors at polarized-growth sites to promote local actin filament polymerization.
- GO:0000133 GO:0000133 defines the polarisome by its role in directing localized assembly of actin filaments at polarization sites.
- DOI:10.1038/s41467-019-13125-1 Xie et al. 2019 dissected Spa2-mediated macromolecular condensation for actin polymerization.

Mechanism graphs

Spa2-centered polarisomes concentrate actin assembly factors (FUNCTION)

In Saccharomyces cerevisiae, the Spa2/Pea2 scaffold localizes to polarized-growth sites, while Bni1 formin and Bud6 act in the Spa2-mediated module that drives local actin-filament assembly.

Subject	Predicate	Object	Evidence
Spa2/Pea2 polarisome scaffold	localizes to	polarisome	`DOI:10.1083/jcb.135.3.725` Valtz and Herskowitz 1996 found Pea2 and Spa2 at sites of polarized growth and established their interdependent localization.
Bni1 formin	supports	actin filament assembly	`DOI:10.1038/s41467-019-13125-1` Xie et al. 2019 modeled Bni1 in the Spa2-mediated actin-polymerization system.
Bud6 actin nucleation-promoting factor	supports	actin filament assembly	`DOI:10.1038/s41467-019-13125-1` Xie et al. 2019 studied Bud6 together with Bni1 around Spa2.
polarisome	directs	actin filament assembly	`GO:0000133` GO:0000133 defines the polarisome by its actin-filament assembly role. `DOI:10.1038/s41467-019-13125-1` Xie et al. 2019 tested Spa2-mediated actin polymerization in the polarisome module.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral family groundings for fungal Spa2/Pea2, Bni1, Bud6/Aip3, and additional polarisome-associated proteins. The initial record uses Saccharomyces names and filamentous-fungal homolog studies to delimit the protein cohorts without guessing InterPro, Pfam, NCBIfam, or UniProtKB family accessions.
CURATION_TODO (OPEN): Curate Aip5 and Myo2 relationships after deciding which are stable polarisome constituents versus associated actin-assembly or transport machinery. Aip5 contributes to Spa2-centered actin polymerization, and Myo2 focuses the complex, but the first record includes only the canonical Bni1/Spa2/Pea2/Bud6 constituents from the GO definition.

Evidence

GO:0000133 Gene Ontology cellular-component term for polarisome.
GO:0031560 Gene Ontology cellular-component term for the cellular bud neck polarisome.
GO:0031561 Gene Ontology cellular-component term for the cellular bud tip polarisome.
GO:0031562 Gene Ontology cellular-component term for the hyphal tip polarisome.
GO:0031563 Gene Ontology cellular-component term for the mating projection tip polarisome.
DOI:10.1083/jcb.135.3.725 Valtz and Herskowitz 1996, 'Pea2 protein of yeast is localized to sites of polarized growth and is required for efficient mating and bipolar budding', Journal of Cell Biology.
DOI:10.1128/MCB.18.7.4053 Sheu et al. 1998, 'Spa2p interacts with cell polarity proteins and signaling components involved in yeast cell morphogenesis', Molecular and Cellular Biology.
DOI:10.1038/s41467-019-13125-1 Xie et al. 2019, 'Polarisome scaffolder Spa2-mediated macromolecular condensation of Aip5 for actin polymerization', Nature Communications.
DOI:10.1083/jcb.202006193 Dunkler et al. 2021, 'Type V myosin focuses the polarisome and shapes the tip of yeast cells', Journal of Cell Biology.
DOI:10.1128/EC.00036-06 Virag and Harris 2006, 'Functional Characterization of Aspergillus nidulans Homologues of Saccharomyces cerevisiae Spa2 and Bud6', Eukaryotic Cell.
DOI:10.1371/journal.pone.0030372 Lichius et al. 2012, 'Comparative Live-Cell Imaging Analyses of SPA-2, BUD-6 and BNI-1 in Neurospora crassa Reveal Novel Features of the Filamentous Fungal Polarisome', PLoS ONE.

Curation history

2026-09-11T05:51:49Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-11T05:53:56Z codex · EXPANDED_RECORD — Added Spa2/Pea2, Bni1, and Bud6 components, fungal distribution, Saccharomyces and Neurospora canonical examples, polarized actin assembly function, GO/DOI evidence, a nonmechanistic Spa2-centered assembly graph, and grounding/boundary TODOs.
2026-09-11T05:59:24Z codex · FIXED_ANCHORS — Replaced bare discussion section anchors with component and causal-graph anchors that resolve to local identifiers.
2026-09-11T06:04:40Z codex · ADDRESSED_REVIEW — Resolved #424, #425, and #426 by narrowing the Saccharomyces example to the Valtz-supported Spa2/Pea2 localization claim, rewriting the Bni1 and Bud6 graph edges as actin-assembly support edges, and removing unsupported Msb3/Msb4 claims from the Aip5/Myo2 boundary TODO.

Source: data/structures/other/polarisome.yaml