Some effects of daunomycin on the nucleic acid synthesis in synchronized L-cells

Abstract

A synchronous cell system, based on the mechanical selection of mitotic cells, is briefly characterized. The mitotic index at the first synchronous division is better than 80%. Prophases constitute 40–55%, metaphases 25–45%, anaphases 1–5%, telophases 5–12%, interphases 4–18% and pyknoses 2–4%. Second synchronous mitotis is reached within 22 hr±10·5% by 96% of the cells. The G 1, S and G 2 phases measured from the incorporation of radioactive-labelled precursors into DNA constitute each 1 3 of the cell cycle. Daunomycin is found to decrease the mitotic index both by action in the interphase and by direct action on mitosis. Also morphological changes are reported and discussed in relation to the phenomenon of unbalanced growth. Some obersvations on the nature of the inhibition of nucleic acid synthesis brought about by daunomycin is discussed in relation to observation time, membrane permeability and cellular fractions. Finally the results of investigations on the sequential inhibition of nucleic acid fractions are reported.