Potential regulatory elements for germline transcription in or near murine Sgamma1

We were interested in identifying cis-acting elements that regulate germline transcription and switch recombination of heavy chain genes. The murine gamma1 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/I exon boundary (termed 'Site I'); we localized a second pair of DNase hypersensitive sites to just 5' of the Sgamma1 region (termed 'Site II'). The DNA region of hypersensitive Site II includes a NF-kappaB/Rel binding site and a STAT6 binding site. It is noteworthy that NF-kappaB and STAT6 are induced by the same agents (CD40 ligation and IL-4 respectively) that stimulate germline transcription and switch recombination of the murine gamma1 gene. Transgenes with the gamma1 promoter region (DNase hypersensitive Site I), Igamma1 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 gamma1 gene, a complete 17 kb gamma1 transgene or a derivative of the 17 kb gamma1 transgene that lacked most of Cgamma1. The promoter/Igamma1/Site II transgenes lacked Sgamma1 and we found that gamma1 transgenes that lacked only Sgamma1 also expressed germline transcripts with proper regulation, but at a low level. This suggested that the Sgamma1 region includes positive elements for regulation of the amount of germline transcripts.