Electrophoresis of positioned nucleosomes

We present in this paper an original approach to compute the electrophoretic mobility of rigid nucleo-protein complexes like nucleosomes. This model allows to address theoretically the influence of complex position along DNA, as well as wrapped length of DNA on the electrophoretic mobility of the complex. The predictions of the model are in qualitative agreement with experimental results on mononucleosomes assembled on short DNA fragments (<400bp). Influence of additional experimental parameters like gel concentration, ionic strength, effective charges is also discussed in the framework of the model, and is found to be qualitatively consistent with experiments when available. Based on the present model, we propose a simple semi-empirical formula describing positioning of nucleosomes as seen through electrophoresis.