Potential regulatory elements for germline transcription in or near murine Sγ1

We were interested in identifying cis-acting elements that regulate germline transcription and switch recombination of heavy chain genes. the murine gamma 1 heavy chain gene includes two DNase I hypersensitive sites, which may represent protein:DNA interactions important for germline transcription and switch recombination. One DNase hypersensitive site is at the promoter/l exon boundary (termed 'Site I'); we localized a second pair of DNase hypersensitive sites to just 5' of the S(gamma)1 region (termed 'Site II'). The DNA region of hypersensitive Site II includes a NF-kappa B/Rel binding site and a STAT6 binding site. It is noteworthy that NF-kappa B and STAT6 are induced by the same agents (CD40 ligation and IL-4 respectively) that stimulate germline transcription and switch recombination of the murine gamma 1 gene. Transgenes with the gamma 1 promoter region (DNase hypersensitive Site I), 1(gamma)1 and DNase I hypersensitive Site II expressed germline transcripts with correct regulation, including IL-4 inducibility, However, the level of stable transcripts produced by the transgenes was much lower than that of the endogenous gamma 1 gene, a complete 17 kb gamma 1 transgene or a derivative of the 17 kb gamma 1 transgene that lacked most of C(gamma)1. The promoter/l(gamma)1/Site II transgenes lacked S(gamma)1 and we found that gamma 1 transgenes that lacked only S(gamma)1 also expressed germline transcripts with proper regulation, but at a low level. This suggested that the S(gamma)1 region includes positive elements for regulation of the amount of germline transcripts.