ECSIT is a ubiquitously expressed protein that plays an important role as an adaptor protein in the cytosolic signal transduction cascade events triggered by Toll receptor activation. It was initially identified as a cytoplasmic protein interacting specifically with TNF receptor associated factor (TRAF)-6 in the TLR pathway. Knockdown of ECSIT results in severely impaired complex I assembly and disturbed mitochondrial function. Recombinant human ECSIT protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.