Mechanisms of DNA entry into mammalian cells. II. Phagocytosis of calcium phosphate DNA co-precipitate visualized by electron microscopy

Electron microscopic and autoradiographic techniques were used to follow the entry of calcium phosphate (Ca-Pi) crystals and co-precipitated DNA into mouse Ltk^- cells. The complex was observed to enter cells primarily by phagocytosis. Filter hybridization experiments and examination of fluorescently-labelled DNA detected intracellular DNA at 2 h after incubation, and the uptake increased linearly to 8 h. Phagocytosis of DNA-Ca-Pi co-precipitate was an energy- and temperature-dependent process and was not observed in ATP-depleted cells or in cells incubated in the cold or in the presence of colcemid.