Bacterial nature of radioactive DNA found in tomato plants incubated in the presence of bacterial DNA-3H

FOREIGN DNA can enter the cell nuclei of tomato plants, but its composition remains largely unaltered1-3. When tritiated bacterial DNA is taken up by tomato plants, all the DNA can be isolated and centrifuged on a caesium chloride gradient. The radioactive molecules are of two kinds: one having the density of the tomato DNA, the other that of the foreign DNA used in the experiment. Thirty to sixty per cent of the radioactive molecules which sediment have the density of the bacterial DNA. Radioactive molecules having the density of tomato DNA have been considered to be bacterial DNA which has been broken down and used for de novo synthesis2.