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Deficit in DNA content relative to histones in X-irradiated HeLa cells
Abstract:
The DNA and histone content of HeLa S-3 cell cultures was measured by direct mass assays 21 hours after 1000 rad of X-irradiation, when the cells were arrested in G2 phase. The nuclear DNA content of such cultures was found to be deficient (73% of control values). In contrast, the synthesis of nuclear histones persisted, and the total histone content was close to 100% of control values. When synchronously-growing cultures were irradiated in mid-S phase and examined 3-5 hours later in G2 phase, both DNA and histone content were equal to control values.
Insights
X-irradiation reduces DNA content in HeLa cells arrested in G2 phase, while histone synthesis continues. However, cells irradiated in S phase show normal DNA and histone levels by G2 phase.
Area of Science:
- Cell Biology
- Radiation Biology
- Molecular Biology
Background:
- Cell cycle progression is tightly regulated.
- DNA damage can induce cell cycle arrest.
- Histones are crucial for DNA packaging and gene regulation.
Purpose of the Study:
- To investigate the impact of X-irradiation on DNA and histone content in HeLa S-3 cells.
- To determine if DNA damage affects histone synthesis during specific cell cycle phases.
Main Methods:
- HeLa S-3 cell cultures were subjected to X-irradiation (1000 rad).
- DNA and histone content were quantified using direct mass assays.
- Cells were analyzed at G2 phase (21 hours post-irradiation) and G2 phase (3-5 hours post-irradiation after S phase exposure).
Main Results:
- Cells arrested in G2 phase 21 hours post-irradiation exhibited a 27% reduction in nuclear DNA content compared to controls.
- Despite DNA reduction, total histone content remained near control levels, indicating persistent histone synthesis.
- Synchronized cells irradiated in mid-S phase showed normal DNA and histone content by G2 phase.
Conclusions:
- X-irradiation in G2 phase leads to DNA deficiency but not histone deficiency in HeLa cells.
- Histone synthesis can persist even when DNA content is compromised.
- The timing of irradiation relative to the cell cycle influences the combined DNA and histone content observed in G2 phase.