ECSIT is a 431 amino acid ubiquitously expressed protein that plays an important role as an adaptor protein in the cytosolic signal transduction cascade events triggered by Toll receptor activation. Within the Toll pathway, ECSIT regulates MEKK1 processing for activation of NFκB, a major event leading to initiation of the innate immune response. In the mitochondria, ECSIT interacts with NDUFAF1 and assists in the formation of NADH:ubiquinone oxidoreductase (complex I), an extremely complicated multiprotein complex located in the inner mitochondrial membrane that functions in the transport of electrons from NADH to ubiquinone. Knockdown of ECSIT results in severely impaired complex I assembly and disturbed mitochondrial function. There are two isoforms of ECSIT that are produced as a result of alternative splicing events