Incorporation of Deoxyribonucleic Acid by Mammalian Cells in vitro

Abstract

TRANSFORMATION of bacterial cells in the presence of deoxyribonucleic acid (DNA) has been demonstrated^1–3, and has indicated that genetic information is carried by DNA. There is little unequivocal evidence for such transformations in higher forms of life, in contrast to the obvious transfer of genetic information that occurs by means of the gamete during fertilization. The two reported attempts to obtain these transformations through the mediation of added DNA have been conflicting^4,5. On the other hand, evidence for the uptake of DNA by mammalian cells^6,7 has supported the idea that observed biological effects might be obtained. In this communication I present evidence for the incorporation of extracellular high molecular weight DNA into the nuclear DNA of cells of the Ehrlich–Lettré ascites tumour, when they are incubated in vitro (Table 1). Labelled homologous DNA for these experiments was first obtained by injecting formate labelled with carbon-14 intraperitoneally in mice bearing this tumour. After an appropriate time-interval, the tumour cells were removed and washed and the DNA isolated by the detergent procedure⁸. To determine the specific activity of the DNA used in the experiments, samples were hydrolysed with 70 per cent perchloric acid for 1 hr. at 100° C. and the bases, adenine and thymine, separated by paper chromatography using a solvent system of ^isopropanol, hydrochloric acid and water. The bases were eluted and the specific activity of each was determined for appropriately plated samples using a gas-flow counter for the radioactivity determinations.