Microscopic analysis of DNA and DNA-protein assembly by transmission electron microscopy, scanning tunneling microscopy and scanning force microscopy

To investigate DNA and DNA-protein assembly, nucleic acids were adsorbed to freshly cleaved mica in the presence of magnesium ions. The efficiency of DNA adhesion and the distribution of the molecules on the mica surface were checked by transmission electron microscopy. In addition, various kinds of DNA-protein interactions including DNA wrapping and DNA supercoiling were analyzed using electron microscopy. In parallel, this Mg2+/mica method can be applied (1) to analyze embedded DNA by scanning tunneling microscopy, (2 ) to visualize freeze-dried, metal coated DNA-protein complexes by tunnelin g microscopy, and (3) to image DNA or DNA-protein interaction in air or in liquid by scanning force microscopy. An advantage of such a correlative app roach is that parallel imaging can reveal complementary information. The be nefit of such a combined approach in analysis of protein-induced DNA bendin g is discussed.