Gel retardation assays. Electrophoretic migration of V5PB pDNA. (A) or mRNA (B) complexed with PEI at varying N/P ratios ranging from 0 to 5. Complexes were prepared by mixing 1 μg of V5PB mRNA or pDNA with different amount of PEI according to the desired ratio. Black arrowhead indicates supercoiled pDNA whereas grey arrowheads indicate different states of condensation of nicked pDNA. Experiments have been done three times.