Fate of foreign DNA in ascites tumor cells

CsCl gradient analysis of the rate of exogenous [³H] labeled DNA in ascites tumor cells shows that these cells take up the foreign material and integrate it with their own DNA as double stranded molecules bound by covalent linkages to the recipient double stranded DNA. This heteroduplex subsequently becomes replicated by the dividing cells and is transmitted to their progeny. In the presence of ATP, the DNA uptake is enhanced 10 times (0.1-0.9% of the endogenous cell DNA). Pentobarbital decreases the incorporation of [³H] thymidine without modifying the uptake of the foreign DNA. In the presence of DEAE dextran the amount of exogenous bacterial DNA found associated with the cells increases, but 96% of this radioactivity can be removed upon DNAase treatment. In X irradiated cells, the uptake of exogenous DNA is stimulated, this stimulation being to some extent dose dependent. When cells are treated with BrdUrd and their DNA analyzed in CsCl gradients, two U.V. peaks are found corresponding to the newly synthesized DNA and to the nonreplicated DNA. If cells are treated with BrdUrd, [¹⁴C] thymidine and [³H] DNA, the [³H] label is found associated only with the nonreplicated DNA while the [¹⁴C] label is found associated with the newly synthesized DNA. It therefore appears that uptake and/or integration of foreign DNA could occur by a mechanism different from normal semiconservative replication.