Different mechanisms have been proposed to explain the specificity of enhancer-promoter interactions, including promoter competition and insulator DNA elements. In the 9 July Proceedings of the National Academy of Sciences, Vincent Calhoun and colleagues propose a different model, involving promoter-proximal tethering elements (Proc Natl Acad Sci USA 2001, 99:9243-9247).

They studied the Antennapedia gene complex (ANT-C) of Drosophila that contains a cluster of homeobox genes. Expression of the Scr selector gene depends on a distal enhancer T1 located 25 kb upstream. In between Scr and T1 lies the pair-ruled gene ftz, which is regulated by the intergenic enhancer AE1. Calhoun et al. attached the Scr and ftz promoter regions to CAT and LacZ reporter genes; they then showed that the core promoter elements were not important for regulating enhancer specificity. Promoter deletion constructs demonstrated that an Scr promoter fragment of 450 bp was sufficient...

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