Functions as an activator subunit for the DBF2 protein kinase. Binds to DBF2, which is required for the phosphorylation and activation of DBF2 by the upstream kinase CDC15 in late anaphase. DBF2-MOB1 is part of the mitotic exit network (MEN) signaling cascade, which regulates release from the nucleus and activity of phosphatase CDC14. Required for inactivation of mitotic cyclin-dependent kinase for exit from mitosis, cytokinesis and G1 gene transcription. Interacts with protein kinase DBF2 to form the MEN DBF2-MOB1 kinase complex. Localizes predominantly to the cytoplasmic surface of the spindle pole body during anaphase and to a ring at the bud neck during cytokinesis. Translocates to the nucleus during mitosis and associates with centromere DNA. Phosphorylated by CDC15. Present with 5020 molecules/cell in log phase SD medium. Belongs to the MOB1/phocein family.