Differential interactions between the immunoglobulin heavy chain mu intron and 3' enhancer

The immunoglobulin heavy chain 3' enhancer may be a novel type of a transcriptional regulation element in as much as its function is position dependent. We show that there are interactions between the mu intron and 3' enhancer which are differentially regulated depending on the distance between the two elements. Thus, a transcriptional repression is exerted by the 3' enhancer when juxtaposed to the intron enhancer. Whereas no or only modest synergism between the immunoglobulin mu intron and 3' enhancer has been reported to date, we show here that the stimulatory effect is substantially increased by extending the distance between the two enhancers. In our stable expression system, the mu intron enhancer insulated the test gene from neighboring chromatin.