MUL1 (Mitochondrial E3 Ubiquitin Protein Ligase-1) is a crucial moderator of RIG-I (Retinoic Acid-Inducible-Gene-I) signaling. This protein is localized to the mitochondria where it interacts with MAVS (Mitochondrial Antiviral Signaling) and catalyzes RIG-I post-translational modifications that inhibit RIG-I-dependent cell signaling. MUL1 contains a unique BAM (Beside A Membrane) domain and a C-terminal RING-finger domain. This protein has been implicated in several processes that occur in animal cells such as NF-KappaB activation, innate immunity and antiviral signaling, suppression of PINK1/parkin defects, mitophagy in skeletal muscle, and caspase-dependent apoptosis.