DNA at membrane surfaces: an experimental overview

Atomic force microscopy studies of DNA attached to rigid surfaces were initially motivated by the development of methods which would stretch DNA for the purposes of rapid sequencing. Currently there is much interest in studies of multilayers of DNA chains self-assembled on membranes which form spontaneously when DNA adsorbs onto oppositely charged cationic liposomes (CLs). A major motivation for elucidating the structures and interactions in these CL-DNA complexes arises for two reasons. The first is that they are known to mimic certain characteristics of viruses by being efficient chemical carriers of genes (DNA sections) for delivery in cells. The second is that they are models of studies of DNA condensation phases in two dimensions. DNA-membrane interactions should also provide clues for the relevant molecular forces in the condensation of DNA in chromosomes and viral capsids. The particular complexes described in this review contain linear DNA forming a new 'hybrid' phase of matter; that is, the DNA chains form a finite size two dimensional smectic coupled to the three dimensional smectic phase of membranes.