Component of the ERMES/MDM complex, which serves as a molecular tether to connect the endoplasmic reticulum and mitochondria (PubMed:19556461). Components of this complex are involved in the control of mitochondrial shape and protein biogenesis, and function in nonvesicular lipid trafficking between the ER and mitochondria (PubMed:8089172, PubMed:9628893, PubMed:27469264). The MDM12-MMM1 subcomplex functions in the major beta-barrel assembly pathway that is responsible for biogenesis of all outer membrane beta-barrel proteins, and acts in a late step after the SAM complex. The MDM10-MDM12-MMM1 subcomplex further acts in the TOM40-specific pathway after the action of the MDM12-MMM1 complex (PubMed:17410204). Essential for establishing and maintaining the structure of mitochondria and maintenance of mtDNA nucleoids (PubMed:11266455, PubMed:12454062, PubMed:14981098). Homodimer (By similarity). Component of the ER-mitochondria encounter structure (ERMES) or MDM complex, composed of MMM1, MDM10, MDM12 and MDM34 (PubMed:13679517, PubMed:17410204, PubMed:19556461). A MMM1 homodimer associates with one molecule of MDM12 on each side in a pairwise head-to-tail manner, and the SMP-LTD domains of MMM1 and MDM12 generate a continuous hydrophobic tunnel for phospholipid trafficking (By similarity). The ERMES/MDM complex localizes to a few discrete foci (around 10 per single cell), that represent mitochondria-endoplasmic reticulum junctions. These foci are often found next to mtDNA nucleoids. The SMP-LTD domain is a barrel-like domain that can bind various types of glycerophospholipids in its interior and mediate their transfer between two adjacent bilayers. Glycosylated. Loss of mitochondrial integrity (PubMed:26370498). Abolishes growth on non-fermentable carbon source (glycerol with ethanol) (PubMed:26370498, PubMed:27280386). Slow growth on fermentable carbon source (glucose) (PubMed:26370498, PubMed:27280386). Synthetic lethal with VPS13 (PubMed:26370498, PubMed:27280386). Normal levels of MMM1 require MDM34. Present with 2490 molecules/cell in log phase SD medium. Belongs to the MMM1 family. Was originally (PubMed:12972421 and PubMed:8089172) proposed to be inserted into either the outer or inner mitochondrial membrane, yet more recent data indicates that it is instead inserted into the ER.