Non-catalytic component of the mitochondrial inner membrane peptidase (IMP) complex. IMP catalyzes the removal of signal peptides required for the targeting of proteins from the mitochondrial matrix, across the inner membrane, into the inter-membrane space. SOM1 facilitates cleavage of a subset of IMP substrates. Component of the mitochondrial inner membrane peptidase (IMP) complex which at least consists of IMP1, IMP2 and SOM1. Present with 358 molecules/cell in log phase SD medium.