DNase I hypersensitive sites (DHSs) and historic acetylation status were examined in the Ig-beta locus of chicken B lymphocyte-derived DT40 cells and liver-derived LMH cells. Twelve DT40-specific DHSs were identified: one in the Ig-beta promoter, one in the first intron of the Ig-beta gene, three in the sodium channel gene located upstream of the -Ig-beta gene, two between the sodium channel gene and the Ig-beta gene, four between the Ig-beta gene and a downstream growth hormone (GH) gene, and one in the downstream region of the GH gene. Transient transfection studies show that the DHS in the intron of Ig-beta gene enhances the activity of the Ig-beta promoter fourfold. A 1.6 kb DNA fragment, which includes two DHSs, from the sodium channel gene enhanced promoter activity threefold. The transcription enhancing ability of the intron DHS was dependent on orientation, but was not promoter specific. Electrophoretic mobility shift assays (EMSA) demonstrated that an Ets protein family member binds to the intron DHS. In DT40 cells, a distinguished acetylation of H3 and H4 histories was found at the Ig-beta promoter, in addition to the enhanced acetylation of both histories at DT40-specific DHSs. (C) 2004 Elsevier B.V. All rights reserved.