interphase SIN signaling complex

GO:0160066 · Cytoskeleton · Multiprotein complex · Proposed

A SIN signaling complex associated with the old spindle pole body during interphase in an inhibitory configuration. In Schizosaccharomyces pombe, the Byr4-Cdc16 GAP inhibits the Spg1 GTPase. Dma1-dependent ubiquitination of the Sid4 scaffold antagonizes Plo1 recruitment in G2 and during a mitotic checkpoint arrest. [DOI:10.1038/emboj.2010.317]

Synonyms: interphase SIN signalling complex

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

Taxonomic distribution

• NCBITaxon:4896 Schizosaccharomyces pombe — COMMON: Fission yeast is the system in which the interphase SIN signaling complex was defined at the old spindle pole body; no broader fungal distribution is asserted here. [DOI:10.1038/emboj.2010.317]

Canonical examples

• NCBITaxon:4896 Schizosaccharomyces pombe — Reference fission-yeast system for the interphase SPB-associated SIN configuration in which Byr4-Cdc16 inhibits Spg1 and Dma1-dependent Sid4 ubiquitination limits Plo1 recruitment in G2 and during mitotic checkpoint arrest. [DOI:10.1038/emboj.2010.317]

Functions

• interphase SIN inactivation — In S. pombe, Byr4-Cdc16 restrains Spg1 during interphase. Dma1-dependent Sid4 ubiquitination limits Plo1 recruitment in G2 and during a mitotic checkpoint arrest, helping prevent premature septation. This inhibitory configuration does not imply that SIN remains inactive throughout normal pre-anaphase mitosis.
  • GO:0160066 GO:0160066 identifies the interphase inhibitory SIN configuration; the local molecular-role and cell-cycle wording follows the primary paper instead of its erroneous Spg1-as-GAP source wording.
  • DOI:10.1038/emboj.2010.317 Johnson and Gould 2011 distinguish the Spg1 GTPase from its Byr4-Cdc16 GAP. Figures 5 and 7 support Dma1-dependent Sid4 ubiquitination antagonizing Plo1 recruitment in G2 and during checkpoint arrest. The Introduction describes Spg1 activation in metaphase, so inhibition is not uniform throughout pre-anaphase mitosis.

Discussions

• INTERPRETATION (RESOLVED): Keep the interphase SIN signaling complex as the narrower fission-yeast GO child rather than the broad SIN/MEN complex or later anaphase SIN states. GO:0160066 is an is-a child of the broader GO:0160065 SIN/MEN signaling complex and is defined by the old-SPB interphase or early-M-phase SIN state. It is distinct from GO:0160067, the new-SPB SIN signaling complex active in anaphase, and from GO:1990334, the narrower two-component GAP complex. No part_of link to the old mitotic SPB is asserted here because GO:0160066 says the complex is associated with that SPB rather than declaring a proper-parthood relation.
• CURATION_TODO (OPEN): Resolve exact source-neutral family groundings for the old-SPB Dma1-linked and Spg1-regulatory constituents of the interphase SIN signaling complex. This first GO-backed record captures the interphase SIN signaling complex without guessing InterPro, Pfam, NCBIfam, UniProtKB, or Complex Portal groundings for fission-yeast-specific protein names.
• INTERPRETATION (RESOLVED): Distinguish the Spg1 GTPase from its GAP and bound interphase/checkpoint inhibition by cell-cycle context. The inherited GO:0160066 definition calls Spg1 a GTPase activator, although the cited primary paper identifies Spg1 as the GTPase inhibited by Byr4-Cdc16. Earlier curation corrected part of the function wording but left the definition and an unrestricted inactive-before-anaphase claim. The paper separates normal cell-cycle progression from G2 and mitotic checkpoint arrests.

Evidence

• GO:0160066 Gene Ontology cellular-component term for the interphase SIN signaling complex, with the British spelling as an exact synonym.
• GO:0160065 Gene Ontology parent term for the broader SIN/MEN signaling complex.
• GO:0071957 Gene Ontology cellular-component term for the old mitotic spindle pole body named in the GO:0160066 definition.
• DOI:10.1038/emboj.2010.317 Johnson and Gould 2011 studied Dma1-dependent Sid4 ubiquitination and Plo1 recruitment at fission-yeast SPBs. G2 and nda3-KM311 checkpoint experiments are distinct from normal metaphase activation; Spg1 is the GTPase and Byr4-Cdc16 its inhibitory GAP.

Curation history

• 2026-09-29T19:21:58Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
• 2026-09-29T19:22:46Z codex · EXPANDED_RECORD — Added the GO exact synonym, SIN/MEN parentage, fission-yeast scope, an interphase SIN-inactivation function, GO and literature evidence, and boundary/component discussions.
• 2026-09-29T19:24:08Z codex · CORRECT_FUNCTION_WORDING — Corrected Spg1 wording so the record describes Spg1-regulatory GAP activity without calling the Spg1 GTPase itself a GAP.
• 2026-10-11T16:16:36Z codex · ADDRESS_SAVED_REVIEW — Addressed #2223: Corrected the inherited Spg1/GAP role error and bounded SIN inhibition to interphase and checkpoint contexts; updated example/evidence and appended a source-conflict clarification without rewriting prior discussions.

Source: data/structures/cytoskeleton/interphase_sin_signaling_complex.yaml