Influence of DNA superstructural features and histones aminoterminal domains on mononucleosome and dinucleosome positioning.

Mononucleosome and dinucleosome positioning was studied in the complexes between two DNA fragments of different lengths, both containing a strongly curved sequence from Crithidia fasciculata kinetoplast, and histone octamers either normal or lacking aminoterminal domains. The results obtained by Exo III and DNase I selective digestion were: (a) The first and most stable nucleosome, formed with both types of histone octamers, is positioned on the curved sequence, showing a multiple dyad axis translational positioning with the same rotational phasing. This result is in very good agreement with the theoretical prediction, obtained by adopting a method developed by us, based on the evaluation of DNA distortion energy from the nucleotide sequence. (b) The second nucleosome has two main different positions. The first one, near the extremity of the DNA fragment opposite to the curved sequence, presents a higher frequency in the case of normal nucleosome, whereas an intermediate position appears populated with a higher frequency in the case of the "tailless' nucleosome.