Study on incorporation of 3H-DNA in the L-cells by means of electron microscopic autoradiography.

Uptake of isologous DNA (labeled with 3H-thymidine) by L-cells was investigated by means of electron microscopic autoradiography. It was found that exogenous 3H-DNA occurred not only in the cytoplasm, but, already from the 1st hr of incubation, permeated as far as in the host cell nuclei. During continuous cultivation, radioactivity established in the nuclei and cytoplasm increases with maximum value after 12 hr incubation. Beginning at the 3rd hr of incubation, in cytoplasma, grain clusters over loci of higher radioactivity were found. After 24 hr incubation, similar grain clusters in L-cell nuclei were observed. In the cytoplasma of the cells, the grains were often determined over or in the vicinity of lysosomes; in the nuclei they were localized predominantly over heterochromatine. The manner of 3H-DNA and 3H-TdR labeling was also compared.