Ribosomal protein S3:: A KH domain subunit in NF-κB complexes that mediates selective gene regulation

NF-kappa B is a DNA-binding protein complex that transduces a variety of activating signals from the cytoplasm to specific sets of target genes. To understand the preferential recruitment of NF-kappa B to specific gene regulatory sites, we used NF-kappa B p65 in a tandem affinity purification and mass spectrometry proteomic screen. We identified ribosomal protein S3 (RPS3), a KH domain protein, as a non-Rel subunit of p65 homodimer and p65-p50 heterodimer DNA-binding complexes that synergistically enhances DNA binding. RPS3 knockdown impaired NF-kappa B-mediated transcription of selected p65 target genes but not nuclear shuttling or global protein translation. Rather, lymphocyte-activating stimuli caused nuclear translocation of RPS3, parallel to p65, to form part of NF-kappa B bound to specific regulatory sites in chromatin. Thus, RPS3 is an essential but previously unknown subunit of NF-kappa B involved in the regulation of key genes in rapid cellular activation responses. Our observations provide insight into how NF-kappa B selectively controls gene expression.