Nucleosomal-length DNA was constructed to contain one of two 10 bp oligopurine-oligopyrimidine sequences, either d(A10.T10) or d(G10.C10). The 146 base pair (bp) sequences were then each tandemly cloned. This allowed for the production of circularly-permuted sequence variants in which the oligopurine tract was located at eight different positions. The permuted sequences were then assayed for their ability to reconstitute into nucleosomes by competitive reconstitution. The results of the assay indicate that the free energy of nucleosome formation differs only by several tenths of a kilocalorie per mole for an oligopurine tract at any position along the DNA, including the central dyad region.