Required for maintenance of normal mitochondrial morphology (PubMed:16754953, PubMed:26071601). Required for PCP1-dependent processing of MGM1 (PubMed:16754953). The UPS1:MDM35 complex mediates the transfer of phosphatidic acid (PA) between liposomes and probably functions as a PA transporter across the mitochondrion intermembrane space (PubMed:26071602, PubMed:26071601, PubMed:26235513). Phosphatidic acid release requires dissociation of the UPS1:MDM35 complex (PubMed:26235513). Phosphatidic acid import is required for cardiolipin (CL) synthesis in the mitochondrial inner membrane (PubMed:26071602). With UPS2, controls the level of cardiolipin in mitochondria (PubMed:19506038). Cardiolipin is a unique phospholipid with four fatty acid chains and is present mainly in the mitochondrial inner membrane where it stabilizes the electron transport chain supercomplex between complexes III and IV through direct interaction of their subunits. Interacts with MDM35 (PubMed:20622808, PubMed:20657548, PubMed:26071602, PubMed:26071601, PubMed:26235513). Found associated with a 170 kDa complex. Lacks the two major intermembrane space-targeting signals, bipartite presequences and cysteine motifs, and import is mediated by another IMS protein, MDM35. Cells show slow growth, fragmented mitochondria and have a 50-fold reduced level of s-MGM1. These defects can be complemented by human PRELI or bypassed by growth on a nonfermentable carbon source. Present with 704 molecules/cell in log phase SD medium. Belongs to the slowmo family.