monopolin complex

GO:0033551 · Other · Multiprotein complex · Proposed

A protein complex required for clamping microtubule binding sites, ensuring orientation of sister kinetochores to the same pole (mono-orientation) during meiosis I. [GO:0033551]

Synonyms: monopolin subcomplex Csm1/Lrs4; Pcs1/Mde4 complex

Part of: kinetochore (GO:0000776)

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
Csm1 monopolin subunit	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	CSM1	UNKNOWN	Named Csm1/Lrs4 core constituent of the budding-yeast monopolin complex. `GO:0033551` GO:0033551 defines Csm1p as a Saccharomyces cerevisiae monopolin-complex subunit. `DOI:10.1016/s1534-5807(03)00086-8` Rabitsch et al. 2003 identified Csm1p among the nucleolar proteins recruited to kinetochores during meiosis I. `DOI:10.1016/j.cell.2010.07.017` Corbett et al. 2010 structurally analyzed monopolin crosslinking of kinetochore components.
Lrs4 monopolin subunit	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	LRS4	UNKNOWN	Named Csm1/Lrs4 core constituent of the budding-yeast monopolin complex. `GO:0033551` GO:0033551 defines Lrs4p as a Saccharomyces cerevisiae monopolin-complex subunit. `DOI:10.1016/s1534-5807(03)00086-8` Rabitsch et al. 2003 identified Lrs4p among the nucleolar proteins recruited to kinetochores during meiosis I. `DOI:10.1016/j.cell.2010.07.017` Corbett et al. 2010 structurally analyzed monopolin crosslinking of kinetochore components.
Hrr25 monopolin subunit	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	HRR25	UNKNOWN	Casein kinase 1 constituent of the budding-yeast monopolin complex. `GO:0033551` GO:0033551 defines Hrr25p as a Saccharomyces cerevisiae monopolin-complex subunit. `DOI:10.1016/j.cell.2006.07.029` Petronczki et al. 2006 linked budding-yeast casein kinase 1 to monopolar attachment of sister kinetochores in meiosis I.
Mam1 monopolin subunit	Protein	part of	Reviewed label only (reviewed name; no accession asserted)	MAM1	UNKNOWN	Named budding-yeast monopolin constituent tied genetically to homolog segregation during meiosis I. `GO:0033551` GO:0033551 defines Mam1p as a Saccharomyces cerevisiae monopolin-complex subunit. `DOI:10.1016/s0092-8674(00)00217-8` Toth et al. 2000 identified monopolin as a kinetochore factor required for segregation of homologs in yeast meiosis I.

Taxonomic distribution

NCBITaxon:4932 Saccharomyces cerevisiae — COMMON: Budding yeast has a Csm1p/Lrs4p/Hrr25p/Mam1p monopolin complex that promotes sister-kinetochore mono-orientation during meiosis I. [GO:0033551]

Canonical examples

NCBITaxon:4932 Saccharomyces cerevisiae — Reference budding-yeast meiosis system in which Csm1p and Lrs4p were identified as forming a monopolin complex with Mam1p at kinetochores. [DOI:10.1016/s1534-5807(03)00086-8]

Functions

sister kinetochore mono-orientation — Monopolin clamps kinetochore microtubule-binding sites so sister kinetochores orient to the same spindle pole during meiosis I.
- GO:0033551 GO:0033551 defines the monopolin complex by sister kinetochore mono-orientation during meiosis I.
- DOI:10.1016/s0092-8674(00)00217-8 Toth et al. 2000 linked budding-yeast monopolin to homolog segregation during meiosis I.
- DOI:10.1016/j.cell.2006.12.040 Monje-Casas et al. 2007 analyzed monopolin control of kinetochore orientation during budding-yeast meiosis.

Mechanism graphs

Monopolin orients sister kinetochores during meiosis I (FUNCTION)

The budding-yeast Csm1p/Lrs4p/Hrr25p/Mam1p monopolin complex acts at kinetochores to coorient sister kinetochores toward the same spindle pole during meiosis I.

Subject	Predicate	Object	Evidence
Csm1 monopolin subunit	assembles into	monopolin complex	`GO:0033551` GO:0033551 names Csm1p among the Saccharomyces cerevisiae monopolin subunits.
Lrs4 monopolin subunit	assembles into	monopolin complex	`GO:0033551` GO:0033551 names Lrs4p among the Saccharomyces cerevisiae monopolin subunits.
Hrr25 monopolin subunit	assembles into	monopolin complex	`GO:0033551` GO:0033551 names Hrr25p among the Saccharomyces cerevisiae monopolin subunits.
Mam1 monopolin subunit	assembles into	monopolin complex	`GO:0033551` GO:0033551 names Mam1p among the Saccharomyces cerevisiae monopolin subunits.
monopolin complex	is part of	kinetochore	`GO:0033551` GO places the monopolin complex under the kinetochore cellular-component branch.
monopolin complex	promotes	sister kinetochore mono-orientation	`GO:0033551` GO:0033551 defines monopolin by the orientation of sister kinetochores to the same pole during meiosis I. `DOI:10.1016/s0092-8674(00)00217-8` Toth et al. 2000 identified monopolin as a kinetochore factor required for homolog segregation in yeast meiosis I.

Discussions

CURATION_TODO (OPEN): Resolve exact source-neutral family groundings and essentiality calls for Csm1, Lrs4, Hrr25 and Mam1 within the budding-yeast monopolin complex. This first record captures the GO-defined budding-yeast subunit set but leaves subunit grounding at reviewed-label-only instead of guessing InterPro, Pfam, NCBIfam or UniProtKB family identifiers.
CURATION_TODO (OPEN): Review whether and how the Schizosaccharomyces pombe Pcs1/Mde4 complex should be represented as an orthologous monopolin branch. GO:0033551 names the Pcs1/Mde4 complex as a narrow synonym of monopolin, but this first record curates the budding-yeast Csm1p/Lrs4p/Hrr25p/Mam1p cohort and leaves the fission-yeast subunit mapping for a focused orthology review.

Evidence

GO:0033551 Gene Ontology cellular-component term for the monopolin complex.
GO:0032991 Gene Ontology cellular-component parent term for protein-containing complexes.
GO:0000776 Gene Ontology cellular-component term for the kinetochore, which contains the monopolin complex.
DOI:10.1016/s0092-8674(00)00217-8 Toth et al. 2000, Functional genomics identifies monopolin: a kinetochore protein required for segregation of homologs during meiosis I, Cell.
DOI:10.1016/s1534-5807(03)00086-8 Rabitsch et al. 2003, Kinetochore recruitment of two nucleolar proteins is required for homolog segregation in meiosis I, Developmental Cell.
DOI:10.1016/j.cell.2006.07.029 Petronczki et al. 2006, Monopolar attachment of sister kinetochores at meiosis I requires casein kinase 1, Cell.
DOI:10.1016/j.cell.2006.12.040 Monje-Casas et al. 2007, Kinetochore orientation during meiosis is controlled by Aurora B and the monopolin complex, Cell.
DOI:10.1016/j.cub.2007.06.044 Gregan et al. 2007, The kinetochore proteins Pcs1 and Mde4 and heterochromatin are required to prevent merotelic orientation, Current Biology.
DOI:10.1016/j.cell.2010.07.017 Corbett et al. 2010, The monopolin complex crosslinks kinetochore components to regulate chromosome-microtubule attachments, Cell.

Curation history

2026-09-18T14:43:04Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-09-18T14:43:52Z codex · EXPANDED_RECORD — Added GO hierarchy, kinetochore parthood, GO monopolin synonymy, four reviewed label-only budding-yeast subunits, Saccharomyces scope, sister-kinetochore mono-orientation function, DOI/GO evidence, a nonmechanistic function graph and subunit-grounding plus fission-boundary TODOs.
2026-09-18T14:44:17Z codex · NARROW_EVIDENCE_SCOPE — Narrowed the Saccharomyces canonical-example note to the Corbett et al. Csm1/Lrs4 structural evidence supported by its row-level reference.
2026-09-18T14:54:47Z codex · ADDRESS_REVIEW — Resolved #1157 and #1158 by narrowing the GO-backed definition to the directly quoted mono-orientation sentence and replacing the Corbett Csm1/Lrs4 structural-core canonical example with the Rabitsch et al. budding-yeast monopolin-complex evidence.

Source: data/structures/other/monopolin_complex.yaml