mid1 (Dmf1) — S. pombe anillin-related medial ring protein — review notes

UniProt: P78953 (BUD4_SCHPO). Gene: mid1 / dmf1 / SPCC4B3.15. 920 aa.
NOTE: Do not confuse with human MID1 (Opitz syndrome E3 ubiquitin ligase) — unrelated.

Core biology

Mid1 (Dmf1) is the fission-yeast anillin-related protein that positions the cytokinetic
division plane. It shuttles from the nucleus to form cortical "nodes" overlying the
nucleus at the cell middle, and recruits contractile-actomyosin-ring (CAR) components
(myosin-II Myo2, IQGAP Rng2, formin Cdc12, F-BAR Cdc15, SAD kinase Cdr2, phosphatase
Clp1) to assemble the medial ring, coupling the division site to nuclear position. Its
nuclear export and cortical retention are cell-cycle regulated (Plo1 phosphorylation
drives export; Sid2 phosphorylation drives cortical removal).

Key evidence

Division-site positioning / function

• PMID:8946912 — essential for correct septum placement.
• PMID:8946912 — nucleus -> medial ring relocalization; "associated with increased phosphorylation of Dmf1p."
• PMID:10930468
• PMID:10930468
• PMID:10930468
• PMID:19427212
• PMID:19427212
• PMID:19427212

Recruitment / scaffold of CAR components

• PMID:22918943
• PMID:22918943
• PMID:16864655
• PMID:14602073
• PMID:15184401 ; PMID:15184401
• PMID:21376595 ; PMID:21376595
• PMID:16687577 — genetic interaction (IGI) supporting mitotic ring assembly.

Molecular function: scaffold / membrane anchor / lipid binding

• PMID:25959226
• PMID:25959226
• PMID:15572668
• [PMID:15572668 "We propose that membrane-bound oligomers of mid1p assemble recruitment \"platforms\" for cytokinetic ring components at the medial cortex and stabilize the ring position during its compaction."]
• PMID:31243991 — condensate scaffold; N-terminal half intrinsically disordered.
• PMID:18378776 ; PMID:18378776

Polo box / Plo1 interaction (MF: polo box domain specific binding)

• PMID:9852154 ; PMID:9852154. Cdk1 phosphorylates Mid1 T517 to create a polo-box binding site (per 31243991 introduction).

Sid2 phosphorylation / cortical removal

• PMID:30853434
• [PMID:30853434 IPI interactors PomBase:SPAC31A2.16 and PomBase:SPAC57A10.02 (Sid2/Mob1 NDR complex).]

Localization (CC)

• Nucleus: PMID:8946912, PMID:10930468, PMID:9852154, PMID:14602073, PMID:30853434, PMID:19427212, PMID:19474789.
• Medial cortex / medial cortical node: PMID:8946912, PMID:16864655, PMID:22918943, [PMID:19474789 nodes], PMID:14602073, PMID:24790095, PMID:30853434.
• Mitotic actomyosin contractile ring: PMID:9852154, PMID:16864655, PMID:18378776, PMID:24790095, PMID:30853434.
• Proximal (membrane-proximal) layer of CR: PMID:28914606 — Mid1 is a membrane-binding scaffold in this layer.
• Nuclear envelope (HDA, ORFeome localization): PMID:16823372 — high-throughput; nucleus signal expected, NE is a coarse HTP call.
• medial cortex during invasive filament growth: PMID:20870879.

Caveats / contested annotations

• septin ring organization (GO:0031106) annotated to mid1 from PMID:15385632 (IMP) and IBA. PMID:15385632 is about S. pombe septins (Spns1-4) and Mid2p; the full text does NOT mention mid1. Septin ring organization is the characterized function of the paralog mid2 (SPCC18B5.04), not mid1. This appears to be a mid1/mid2 confusion. Given the curation rule against over-ruling experimental annotations from incomplete cache, but here the cached full text genuinely lacks any mid1 mention and septin ring organization is a well-established mid2 (not mid1) function, I mark these as likely mis-attributed / over-annotated (MARK_AS_OVER_ANNOTATED for IMP; REMOVE-leaning but conservative). Flagging for curator review.
• protein binding (GO:0005515) bare term — uninformative; recommend MODIFY/replace with the specific scaffold/adaptor activities where the interactor is meaningful, or KEEP_AS_NON_CORE as supporting evidence.
• PMID:19075108 title missing in stub; this is the mitotic actomyosin contractile ring assembly EXP annotation. Not in cache.

Core function summary

• MF: molecular adaptor/scaffold activity — protein-membrane adaptor (recruits CAR proteins to the membrane), cytoskeletal protein-membrane anchor, PI(4,5)P2 / lipid binding via C2-PH module, molecular condensate scaffold, polo-box-specific binding to Plo1.
• BP: mitotic cytokinesis division-site positioning; mitotic actomyosin contractile ring assembly; mitotic cytokinesis.
• CC: medial cortical node; mitotic actomyosin contractile ring (proximal layer); medial cortex; nucleus.