To clarify the mechanisms and factors involved in the regulation of mouse IL-2R beta gene expression, we isolated the 5'-flanking region of IL-2R beta gene and investigated the promoter activity. Here we elucidated the positive regulatory regions, the most potent of which are located between -50 to -30 bp and -164 to -135 bp. These regions contain a potentially functional Ets and Egr-1-binding sites whose mutations abrogate promoter activity. Data from electrophoretic mobility shift assay indicate that Ets and Egr-1, but not Sp1, bind to the positive regulatory regions, -50 to -30 bp and -164 to -135 bp, respectively. Furthermore, recruitment of Ets and Egr-1 at endogenous IL-2R beta promoter segments in an IL-2-dependent F7 cells was verified by the chromatin immunoprecipitation assay. This study for the first time delineates the molecular mechanisms underlying regulation of mouse IL-2R beta gene transcription by Ets family proteins, partially with Egr-1, and thereby further elucidates the molecular basis of lymphocyte activation and differentiation. (c) 2005 Elsevier Inc. All rights reserved.