Effects of DNA sequence and conformation on nucleosome formation.

A simple theoretical analysis of the free energy balance controlling nucleosome formation shows that the specific effects of different DNA sequences and/or conformations observed in vitro are mainly due to their different elastic properties. A calculation of the elastic free energy required to fold DNA on histone octamers yields quantitative results rationalizing the experimental findings provided that: (i) the average helical repeat of DNA on nucleosomes is greater than 10.2 bp per turn, and (ii) poly[dG.dC] adopts an A-type conformation.