Specific interaction between enhancer-containing molecules and cellular components.

Using an in vivo assay, we have obtained competition between several types of enhancer-containing molecules for cellular components that interact with them. The presence of these cellular factors is required for enhancer function. Specific competition involved enhancers and not other SV40 promoter elements such as the 21 bp repeats or TATA box. Point mutants within the 72 bp repeat of SV40 that were defective in enhancer function were unable to compete for the cellular components in the competition assay. Although heterologous enhancers compete in several types of cells for the same set of cellular molecules, the host cell preference of different enhancers is reflected in the competition assay. This result might explain the previously described host cell preference of enhancer elements.