The main role of the sequence-dependent DNA elasticity in determining the free energy of nucleosome formation on telomeric DNAs

Using a competitive reconstitution assay, we measured the free energy spent in nucleosome formation of eight telomeric DNAs, differing in sequence and /or in length. The obtained values are in satisfactorily good agreement wit h those derived from a theoretical model that allows the calculation of the free energy of nucleosome formation on the basis of sequence-dependent DNA elasticity, using a statistical thermodynamic approach. Both theoretical a nd experimental evaluations show that telomeres are characterized by the hi ghest free energies of nucleosome formation among all the DNA sequences so far studied. The free energy of nucleosome formation varies according to th e different telomeric sequences and the length of the fragments. Theoretica l analysis and experimental mapping by lambda exonuclease show that telomer ic nucleosomes occupy multiple positions spaced every telomeric repeat. Seq uence-dependent DNA elasticity appears as the main determinant of the stabi lity of telomeric nucleosomes and their multiple translational positioning. (C) 1999 Elsevier Science B.V. All rights reserved.