Cloning of RκB, a novel DNA-binding protein that recognizes the interleukin-2 receptor α chain κB site

Transcriptional activation of the interleukin-2 receptor α (IL-2Rα) gene in T cells is dependent on a regulatory element that can bind NF-κB but differs in sequence and function from the κB site of the immunoglobulin (Ig) enhancer. To define the molecular basis of gene-specific regulation by this variant κB site, we have used electrophoretic mobility shift assays to characterize a novel gene product, designated RκB, that binds preferentially to the related κB site in IL-2Rα. A cDNA encoding this 107-kD protein has been isolated from a λgt11 expression library by screening with a probe containing the IL-2Rα κB site. RκB is a tissue-specific transcription factor that contains an amino acid sequence similar to a discrete region of the myogenic regulatory protein myoD, but is unrelated to other DNA-binding proteins, including those belonging to the rel/dorsal gene family. This novel κB binding protein may therefore contribute to the regulation of distinct cellular and viral genes with variant κB sites.