Negative Regulation Contributes to Tissue Specificity of the Immunoglobulin Heavy-Chain Enhancer

We have identified in and around the immunoglobulin heavy-chain enhancer two apparently distinct negative regulatory elements which repress immunoglobulin H enhancer, simian virus 40 enhancer, and heterologous promoter activity in fibroblasts but not in myeloma cells. We propose that in nonlymphoid cells, negative regulatory elements prevent activation of the immunoglobulin H enhancer by ubiquitous stimulatory trans-acting factors.