mating projection tip polarisome

GO:0031563 · Other · Multiprotein complex · Proposed

Protein complex that has a role in determining cell polarity, found at the tip of the mating projection in unicellular fungi exposed to mating pheromone. [GO:0031563]

Part of: mating projection tip (GO:0043332)

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	Scaffold proteins that localize to polarized-growth sites and support periodic mating-projection growth. `DOI:10.1083/jcb.135.3.725` Valtz and Herskowitz 1996 found Pea2 and Spa2 at sites of polarized growth in budding and mating Saccharomyces cells. `DOI:10.1083/jcb.200307065` Bidlingmaier and Snyder 2004 assayed Spa2 and Pea2 during pheromone-induced mating-projection initiation and termination cycles.
Bni1 formin	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	BNI1	CONDITIONAL	Formin effector in the Spa2/Pea2 polarisome module that supports mating-projection initiation. `GO:0000133` GO:0000133 names Bni1p as a Saccharomyces polarisome protein. `DOI:10.1083/jcb.200307065` Bidlingmaier and Snyder 2004 tested Bni1 with Spa2 and Pea2 in pheromone-treated budding yeast.
Bud6/Aip3 actin nucleation-promoting factor	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	BUD6, AIP3	CONDITIONAL	Canonical Saccharomyces polarisome actin nucleation-promoting factor that was tested in periodic mating-projection assays. `GO:0000133` GO:0000133 lists Bud6p among Saccharomyces polarisome proteins. `DOI:10.1083/jcb.200307065` Bidlingmaier and Snyder 2004 treated Bud6 as a known polarisome component and found that bud6 deletion did not change the frequency or morphology of pheromone-induced mating projections.

Taxonomic distribution

NCBITaxon:4932 Saccharomyces cerevisiae — VARIABLE: Budding-yeast polarisome proteins function at the mating-projection tip in pheromone-treated haploid cells. [DOI:10.1083/jcb.200307065]

Canonical examples

NCBITaxon:4932 Saccharomyces cerevisiae — Pheromone-treated budding-yeast model in which Spa2, Pea2, and Bni1 polarisome proteins control mating projection initiation or termination timing. [DOI:10.1083/jcb.200307065]

Functions

mating-projection growth control — The shmoo-tip polarisome positions polarity machinery at the projection apex and supports pheromone-induced projection initiation and termination cycles.
- GO:0031563 GO:0031563 defines the mating projection tip polarisome by its role in determining cell polarity at the projection tip.
- DOI:10.1083/jcb.200307065 Bidlingmaier and Snyder 2004 showed that Spa2, Pea2, and Bni1 regulate periodic mating-projection formation.

Mechanism graphs

Shmoo-tip polarisome topology (FUNCTION)

Spa2/Pea2 scaffold and Bni1 formin proteins act in a polarisome at the mating-projection tip during pheromone-induced polarized growth.

Subject	Predicate	Object	Evidence
Spa2/Pea2 polarisome scaffold	localizes to	mating projection tip polarisome	`DOI:10.1083/jcb.135.3.725` Valtz and Herskowitz 1996 localized Pea2 and Spa2 to polarized-growth sites in budding and mating cells. `DOI:10.1083/jcb.200307065` Bidlingmaier and Snyder 2004 treated Spa2 and Pea2 as polarisome components during mating-projection formation.
Bni1 formin	supports	mating projection formation	`DOI:10.1083/jcb.200307065` Bidlingmaier and Snyder 2004 showed that Bni1, Spa2, and Pea2 regulate mating-projection initiation timing.
mating projection tip polarisome	localizes to	mating projection tip	`GO:0031563` GO:0031563 defines the polarisome as localized to the mating projection tip.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral family groundings for Spa2/Pea2, Bni1, and Bud6 at the mating projection tip. This localized record deliberately reuses the reviewed-label-only Saccharomyces polarisome cohorts from the broader polarisome record instead of guessing InterPro, Pfam, NCBIfam, or UniProtKB family groundings for proteins whose broader homologous families do not exactly delimit the mating-projection-tip complex.
INTERPRETATION (RESOLVED): Keep Cdc42 regulators and Fus1/Fus2 outside the mating-projection-tip polarisome component boundary. Bidlingmaier and Snyder 2004 assayed Cdc24, Bem3, Fus1, and Fus2 together with polarisome mutants during mating-projection cycling, but the exact GO:0031563 structure denotes the localized polarisome complex rather than every Cdc42 regulator or cell-fusion protein that affects projection initiation or termination.
INTERPRETATION (RESOLVED): Retain Bud6/Aip3 as a constituent without asserting a periodic mating-projection phenotype edge. GO:0000133 and the broader polarisome record include Bud6/Aip3 in the canonical Saccharomyces polarisome boundary. Bidlingmaier and Snyder 2004 tested bud6 deletion in the same pheromone-induced projection assay but reported that it did not affect projection frequency or morphology, so Bud6 is retained as a constituent and left out of the first phenotype graph until a precise localized Bud6 edge is curated.

Evidence

GO:0031563 Gene Ontology cellular-component term for the mating projection tip polarisome.
GO:0000133 Gene Ontology cellular-component term for polarisome.
GO:0043332 Gene Ontology cellular-component term for the mating projection tip.
DOI:10.1083/jcb.200307065 Bidlingmaier and Snyder 2004, 'Regulation of polarized growth initiation and termination cycles by the polarisome and Cdc42 regulators', Journal of Cell Biology.
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.

Curation history

2026-09-28T18:19:35Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-28T18:21:18Z codex · EXPANDED_RECORD — Added polarisome parentage, mating-projection-tip parthood, Spa2/Pea2 and Bni1 constituents, Saccharomyces distribution and canonical example evidence, a mating-projection growth function, a nonmechanistic shmoo-tip topology graph, and grounding and boundary discussions.
2026-09-28T18:37:37Z codex · FIXED_DISCUSSION_ANCHORS — Replaced an unresolved bare components discussion anchor with the Spa2/Pea2 and Bni1 component anchors.
2026-09-28T19:09:34Z codex · ADDRESSED_REVIEW — Resolved #1736 by adding Bud6/Aip3 as a reviewed-label-only Saccharomyces polarisome constituent, expanding the grounding TODO, and recording why Bud6 is not asserted in the first mating-projection phenotype graph.
2026-09-28T19:10:24Z codex · REFINED_REVIEW_FIX — Updated the grounding TODO evidence note so #1736's added Bud6 component is reflected in the Bidlingmaier and Snyder evidence.

Source: data/structures/other/mating_projection_tip_polarisome.yaml