On its upstream side, the human interferon-beta gene is flanked by a 7-kb SAR (scaffold-attached region) DNA element. The core of this element is determined and subjected to in vitro reassociations with isolated scaffolds. Binding properties of SAR fragments with decreasing length are quantified and related to consensus sequences like the topoisomerase II box and an ATATTT motif. Characteristics as the stoichiometry, affinity, and cooperativity of the binding process are shown to depend on the length of SAR DNA and suggest a model involving a multiple-site attachment to protein scaffolds. We propose a rational approach for predicting the SAR mediated transcriptional enhancements in vivo from their binding properties in a standardized in vitro assay. The efficiency of this approach is demonstrated for a marker (huIFN-beta) and a selector gene (neor).