Scaffold protein that anchors the contractile ring (CR) at the cell equator during cytokinesis (PubMed:8946912, PubMed:9852154, PubMed:10930468, PubMed:12186944, PubMed:17140794, PubMed:16864655, PubMed:17077120, PubMed:19427212, PubMed:19474789, PubMed:22888038, PubMed:22427686, PubMed:22298427, PubMed:22918954, PubMed:23149940, PubMed:28605916, PubMed:25959226). At the onset of mitosis, membrane-bound oligomers of mid1 assemble recruitment platforms for cytokinetic ring components at the medial cortex and stabilize the ring position during its compaction (PubMed:8946912, PubMed:9852154, PubMed:10930468, PubMed:12186944, PubMed:17140794, PubMed:16864655, PubMed:17077120, PubMed:19474789, PubMed:28605916, PubMed:25959226, PubMed:15572668). Recruits dephosphorylated myo2, but also rng2, clp1 and cdc15 to nodes and to place cytokinetic nodes around the cell equator the medial cortex to promote the ring assembly in cooperation with F-actin (PubMed:15184401, PubMed:18378776, PubMed:21376595, PubMed:21376600, PubMed:22918943). Necessary to stabilize the mitotic spindle perpendicular to the axis of cell division (PubMed:15014440). Recruits also the cdr2 kinase to the CR (PubMed:19474789, PubMed:24982431, PubMed:28605916). In the nucleus, binds to the promoter regions of M-G1 transcribed genes to negatively regulate their expression. Homodimer (PubMed:15572668, PubMed:25959226). Interacts with blt1 and cdr2 (PubMed:19474789, PubMed:23149940, PubMed:24982431). Interacts with gef2 (PubMed:22298427). Interacts with plo1 and rng2 (PubMed:21376600). Interacts with fhk2 and sep1 (PubMed:21098635). Interacts with clp1 (PubMed:18378776). During interphase, is exported from the nucleus and relocates to medial ring at the cell cortex (PubMed:12186944, PubMed:16864655, PubMed:19427212, PubMed:19474789). The localization to the cell division plane is regulated by the cell-end factor pom1 (PubMed:17140794, PubMed:17077120). First forms a diffuse cortical band during spindle formation and then coalesces into a ring before anaphase (PubMed:9852154). Binding to the medial cortex is facilitated by gef2 (PubMed:22298427). Phosphorylation by sid2 leads to removal from the cortex (PubMed:28605916). The cortical ER network restricts the lateral motion of mid1 and hence generates a permissive zone for actomyosin ring assembly precisely at the cell equator (PubMed:20434336). The N-terminal part (residues 1 to 452) is intrinsically disordered but moderately compact and is able to demixe into liquid droplets at concentrations far below its concentration in cytokinesis organizing centers (also called nodes); these physical properties are appropriate for scaffolding other proteins in nodes (PubMed:31243991). The N-terminus has the ability to associate faintly with the medial cortex and is sufficient to form tight rings (PubMed:15572668, PubMed:22427686). This domain is responsible for oligomerization that may contribute to the activity of mid1 as a scaffold for other proteins in cytokinetic nodes and contractile rings (PubMed:22918954). The C-terminus contains a cryptic lipid-binding C2 domain and a PH domain, and is involved in the anchorage to membranes, which stabilizes cytokinetic ring position. The nuclear localization sequence (NLS) is required for nuclear import, whereas both leucine-rich nuclear export sequences NES1 and NES2 are required for nuclear export. Phosphorylated (PubMed:18257517, PubMed:8946912). At the onset of mitosis, becomes hyperphosphorylated, leaves the nucleus, and forms a medial ring (PubMed:8946912). Phosphorylation by plo1 and other kinases may contribute to solubilizing mid1 for export from the nucleus (PubMed:21376600) (Probable). Phosphorylation by sid2 drives removal from the cortex at the actomyosin contractile ring constriction onset (PubMed:28605916).