IntroductionThe phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase is a multiprotein complex with both membranebound and cytosolic components. Flavocytochrome b, the membrane-bound component of the oxidase complex, is a heterodimer composed of a 22-kDa polypeptide subunit (termed p22 phox ) and a 91-kDa glycoprotein subunit (gp91 phox ). 1 NADPH oxidase activation requires assembly of the flavocytochrome b with several cytosolic proteins, including p47 phox , p67 phox , p40 phox , and a GTP-binding protein, either rac1 in macrophages or rac2 in neutrophils. 2 The activated complex generates large quantities of superoxide and other reactive oxygen species essential for the microbicidal function of phagocytes.Molecular genetic defects affecting components of the NADPH system lead to chronic granulomatous disease (CGD), a primary immunodeficiency characterized by early onset of severe recurrent infections. 1 The genes CYBB and NCF1 are the most frequent sites of mutations (ϳ60% and 30% of the cases) leading, respectively, to the X-linked and one of the autosomal forms of CGD. 3,4 The CYBB gene (MIM 306400), encoding gp91 phox , is localized at chromosome Xp21.1 and contains 13 exons spanning 30 kilobases (kb). 5 The CYBB promoter region includes several cis-elements involved in gene regulation by interferon-␥ (IFN-␥) and tumor necrosis factor-␣ (TNF-␣). 6 Several trans-activators and repressors have also been characterized. Removal of repressor elements permits interactions of both widely expressed and IFN-␥-responsive transcriptional activators with cognate binding sites in the CYBB proximal promoter. 7,8 The NCF1 gene (MIM 608512) is localized at chromosome 7q11.23 and encodes p47 phox , a cytosolic component of the oxidase. 3 Li et al 9 characterized the NCF1 promoter and identified a functional binding site for the transcriptional factor PU.1. Further experiments confirmed that differentiationdependent up-regulation of NCF1 gene transcription is associated with changes in PU.1 phosphorylation and increased binding affinity. 10 The transcription factor nuclear factor-B (NF-B) is a heterodimer formed from members of the mammalian rel gene family, which includes p105/p50, p100/p52, p65 (RelA), RelB,12 The general mechanism of activation of the conventional and most common NF-B complex (p50/RelA) starts with its sequestration in the cytoplasm by interaction with a family of inhibitory proteins, termed IBs, including IB␣, IB, IB␥, IBε, and the proto-oncogene Bcl-3. Activation by extracellular signals induces phosphorylation of IB by specific IB kinases (IK␣ and IK) on critical serine residues, Ser32 and Ser36, within the N-terminal signal response domain. 13 IB phosphorylation leads rapidly to its ubiquitinization and rapid proteolytic degradation, thus releasing the NF-B heterodimer to move into the cell nucleus. There it interacts with Bresponsive promoter elements to modulate transcription of The online version of this article contains a data supplement.The publication costs of this article w...