DISTAL ENHANCER REGULATION BY PROMOTER DEREPRESSION IN TOPOLOGICALLY CONSTRAINED DNA IN-VITRO

Long-range promoter-enhancer interactions are a crucial regulatory fea ture of many eukaryotic genes yet little is known about the mechanisms involved. Using cloned chicken beta(A)-globin genes, either individua lly or within the natural chromosomal locus, enhancer-dependent transc ription is achieved in vitro at a distance of 2 kb with developmentall y staged erythroid extracts. This occurs by promoter derepression and is critically dependent upon DNA topology. In the presence of the enha ncer, genes must exist in a supercoiled conformation to be actively tr anscribed, whereas relaxed or linear templates are inactive. Distal pr otein-protein interactions in vitro may be favored on supercoiled DNA because of topological constraints. In this system, enhancers act prim arily to increase the probability of rapid and efficient transcription complex formation and initiation. Repressor and activator proteins bi nding within the promoter, including erythroid-specific GATA-1, mediat e this process.