Purification of protein–DNA complexes by native gel electrophoresis for electron microscopy study

Abstract

Electrophoretic separation under native conditions may be used for purification of protein molecules and their complexes with DNA and other ligands. Here, we employed this approach to separate protein-DNA complexes with a molecular weight of approximately 200 kDa: mono- and dinucleosomes. The purified mononucleosomes were subjected to single particle electron microscopy study using negative stain contrasting, and the two-dimensional projections of the nucleosomes at 25 Å resolution were obtained. A comparison of the nucleosome projections before and after separation in the native PAGE revealed different orientation of particles on the carbon film.