Transmission EM of CFBE41o- cells transfected at the optimal lipid/DNA ratio (6+/1-) and fixed 72 h after the start of transfection. (A)-(C) large membrane-bound vesicles containing aggregates of labelled complexes in the perinuclear region of transfected cells. Destabilization of an early endosome (D), late endosome (E) and membrane-bound vesicles (F and G) by lipid/DNA complexes; (G) a higher magnification of (F). Arrows indicate a part of the aggregated complexes extruded into the cytoplasm and not surrounded by an endosome or a large vesicle membrane. ee: early endosome; g: Golgi apparatus; le: late endosome; mbv: membrane-bound vesicle; ly: lysosome; n: nucleus. Bars: (A)-(C): 1 μm; (D)-(G)): 200 nm.