The surface of the DNA-containing particle is responsible for cell binding and entry. To enter their hosts, many viruses and bacteria divert the function of cell–matrix and cell–cell anchoring proteins, such as heparan sulfate proteoglycans (HSPGs) and integrins. HSPGs are responsible for cell entry of species as
different as Chlamydia trachomatis bacterium [7], adeno-associated virus [8], but also cationic proteins such as bFGF [9], or TAT [10]. Condensed DNA particles also require a cationic surface for transfection to be efficient [11] and their cell entry is mediated by electrostatic interaction with HSPGs at the cell surface [12–14]. This is presumably true for all polycations, whether calcium phosphate-precipitated DNA or cationic peptide-tagged proteins and polynucleotides.