THE EFFECTS OF LOW CONCENTRATIONS OF ACTINOMYCIN D ON THE PROGRESS OF CELLS THROUGH THE CELL CYCLE

The progress of L-cells through the cell cycle in asynchronous and in synchronous culture has been studied at a concentration of actinomycin D which mediates an apparently‘nucleolar-specific’inhibition of RNA synthesis. Under such conditions, cells may be blocked or seriously delayed in the G₁ and G₂ phases of the cycle whilst the processes of DNA synthesis and mitosis once initiated, can still occur at control rates. The results show that the sensitivity of a cell to these blocks depends critically upon the position of that cell within the cycle at the time of drug addition. The possible mechanisms of the drug's action are discussed.