ECSIT homolog (ECSIT) is a ubiquitously expressed protein which has a vital role as an adaptor protein in the cytosolic signal transduction cascade events triggered by Toll receptor activation. ECSIT promotes proteolytic activation of MAP3K1. ECSIT is also involved in the BMP signaling pathway. ECSIT is essential for normal embryonic development. ECSIT was originally classified as a cytoplasmic protein interacting specifically with TNF receptor associated factor (TRAF)-6 in the TLR pathway. ECSIT gene knockdown results in gravely impaired complex I assembly and disrupted mitochondrial function.