Tumor necrosis factor (TNF) receptor associated factors (TRAFs) are the major signal transducers for the TNF receptor superfamily and the interleukin-1 receptor/Toll-like receptor (IL-1/TLR) superfamily (1). TRAF3 was first identified by its interaction with CD40 and the Epstein-Barr virus transforming protein LMP1 (2,3). Several TRAF3 mRNA splice variants exist and some of these can activate the transcription factor NF-kappaB (4). Besides CD40, TRAF3 also interacts with the TRFR superfamily member lymphotoxin-beta receptor (LTbetaR) in association with TRAF2 and the apoptosis inhibitors cIAP1 and Smac. It has been suggested that TRAF3 induces mitochondria-mediated apoptosis upon binding of the TNF family cytokine LIGHT by LTbetaR (5).Synonyms: CAP-1, CAP1, CD40 receptor-associated factor 1, CD40-binding protein, CD40BP, LAP1, LMP1-associated protein, TNF receptor-associated factor 3