Cloning of R kappa B, a novel DNA-binding protein that recognizes the interleukin-2 receptor alpha chain kappa B site

Transcriptional activation of the interleukin-2 receptor alpha (IL-2R alpha) gene in T cells is dependent on a regulatory element that can bind NF-kappa B but differs in sequence and function from the kappa B site of the immunoglobulin (Ig) enhancer. To define the molecular basis of gene-specific regulation by this variant kappa B site, we have used electrophoretic mobility shift assays to characterize a novel gene product, designated R kappa B, that binds preferentially to the related kappa B site in IL-2R alpha. A cDNA encoding this 107-kD protein has been isolated from a lambda gt11 expression library by screening with a probe containing the IL-2R alpha kappa B site. R kappa B 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 kappa B binding protein may therefore contribute to the regulation of distinct cellular and viral genes with variant kappa B sites.