The high resolution structure of the nucleosome core particle of chromatin reveals the form of DNA that is predominant in living cells and offers a wealth of information on DNA binding and bending by the histone octamer. Recent studies imply that chromatin is highly dynamic. This propensity for unfolding and refolding stems from the structural design of the nucleosome core. The histone-fold motif, central to nucleosome structure, is also found in other proteins involved in transcriptional regulation.