Changes in the Quantitative Composition of the Population in Delayed Periods After γ-Radiation Exposure of the Cells in Various Phases of S Period of the First Mitotic Cycle

Using the autoradiographic method, we studied the kinetics of DNA synthesis over the mitotic cycle in mouse corneal epithelium cells in delayed periods after γ-irradiation in different points of the S phase of the first mitotic cycle. The index labeled cells during 1-3 periods of DNA synthesis most adequately reflects quantitative changes in the cell population composition after cell exposure during the first S period. The relative number of labeled S phase cells in the second mitotic cycle in experiments where the cells were irradiated in the S₁ phase of the first S period was 4-fold lower than in experiments where the cells were exposed during S₂ phase. This effect is determined by inhibition of the transcription factors activation. It seems that two territorially different sites of the genome controlling the regulatory stimuli and involved in modification of the quantitative composition of the population are responsible for changes in its quantitative balance.