FIG. 1.

Effect of X rays on viability and cell cycle profile in Rat-1 cells. (A) X-ray (12 Gy) treatment does not cause apoptosis in Rat-1 cells, shown by the absence of cells with a sub-G₁ content (M1). In contrast, UVC treatment (20 J/m²) results in apoptosis, with more than 30% of the cells exhibiting a sub-G₁ DNA content. (B) X-ray treatment has little effect on the cell cycle distribution in Rat-1 cells at either 7 or 24 h after irradiation. Although there appears to be a minor accumulation in G₂, there is no G₁ arrest and cells continue to cycle into S phase.