E3 ubiquitin-protein ligase SIAH1（SIAH1) belongs to the SIAH（seven in absentia homolog) family. SIAH1 is a tumor suppressor protein， which is expressed in intestinal epithelium and activated during apoptosis. SIAH1 is involved in ubiquitination and proteasome-mediated degradation of specific proteins. SIAH1 is comprised of an N-terminal RING-finger domain（required for proteolysis) and a cystein-rich C-terminal domain（which regulates oligomerization and SIAH binding to target proteins). SIAH1 causes indirect degradation of beta-catenin by way of creation of a complex with Siah-interacting protein（SIP)， Skp1 and Ebi.
