Epstein-Barr virus (EBV) latent infection membrane protein 1 (LMP1), a constitutively aggregated and activated pseudoreceptor, activates IFN regulatory factor 7 (IRF7) through RIP1. We now report that the LMP1 cytoplasmic carboxyl terminal amino acids 379 -386 bound IRF7 and activated IRF7. IRF7 activation required TRAF6 and RIP1, but not TRAF2 or TRAF3. LMP1 Y384YD386, which are required for TRADD and RIP1 binding and for NF-B activation, were not required for IRF7 binding, but were required for IRF7 activation, implicating signaling through TRADD and RIP1 in IRF7 activation. Association with active LMP1 signaling complexes was also critical for IRF7 activation because (i) a dominant-negative IRF7 bound to LMP1, blocked IRF7 association and activation, but did not inhibit LMP1 induced NF-B or TBK1 or Sendai virus-mediated IFN stimulated response element activation; and (ii) two different LMP1 transmembrane domain mutants, which fail to aggregate, each bound IRF7 and prevented LMP1 from binding and activating IRF7 in the same cell, but did not prevent NF-B activation. Thus, efficient IRF7 activation required association with LMP1 CTAR2 in proximity to LMP1 CTAR2 mediated kinase activation sites. LMP1 has a 24-aa cytoplasmic N-terminus, six hydrophobic transmembrane domains (amino acids 25 to 186) and a 200-aa cytoplasmic C-terminus (amino acids 187 to 386). The transmembrane domains induce LMP1 aggregation in plasma membrane lipid rafts and barges and constitutively activate two C-terminal cytoplasm signaling domains referred to as C-terminal activation regions (CTAR) or transformation effector sites (TES) 1 and 2, which were initially defined as amino acids 187-231 and 352-386, respectively (Fig. 1A) (2-9). CTAR1 amino acids 201 to 210 engage tumor necrosis factor receptor (TNFR)-associated factors (TRAFs) 1, 3, 2, and 5 and CTAR2 amino acids 376-386 engage TNFRassociated death domain proteins TRADD and RIP1 (4-12). Both signaling domains activate NF-B, p38 mitogen-activated protein kinase (MAPK), and c-Jun N-terminal kinase, thereby altering cell gene expression, cell survival, and immune responses (13-17).LMP1 also induces and activates IFN regulatory factor 7 (IRF7) (18-20), a critical transcription factor for type 1 IFN (IFN)-mediated innate and adaptive immune responses (21-24). IRF7 is comprised of DNA binding, constitutive activation, virus activated, inhibitory, and signal response domains and is activated by serine 477 and 479 phosphorylation (25). Although IRF7 is expressed at low levels in nonstimulated cells, IRF7 is critical for type I IFN expression, particularly in plasmacytoid dendritic cells (24,26,27). Toll-like receptor activation, LMP1 expression, viral infection, and other signals that activate IRF3 and induce IFN  (IFN), can up-regulate IRF7 expression (18, 21-24, 28, 29). IRF7 can bind and localize to MyD88 until ligand-activated Toll-like receptors 7, 8, or 9 engage MyD88 and activate IRF7, which enters the nucleus and up-regulates IFN stimulated response elements (ISREs) to activate I...