Effect of Irradiation on DNA Synthetic Period of the Mitotic Cycle in Cells

Abstract

Kinetics of DNA synthesis in mitotic cycle of mouse corneal epithelial cells after single γ-irradiation (4 Gy) at the end of S period was studied by the method of radioautography. Normally, S period of corneal epithelial cells consists of several stages separated by intervals without DNA synthesis. The estimated mean duration of the first (S(1)) and second (S(2)) phases of S period was 16 and 10 h, respectively, and the interval between them was 7 h. Single irradiation at the end of S period changed the duration of mitotic cycle periods: S(2) phase became 2.2-longer than S(1) phase and the duration of g(1) period decreased, because the time for reparation in irradiated cell increases at the expense of g(1) period. Shortening of g(1) period is a factor promoting the appearance of transformed cells.

Reparation as a Factor Contributing to Genetic Variability of the Biological System

“…This wavy pattern is probably related to the phenomenon of DNA synthesis discontinuity in the eukaryotic cells [7][8][9][10][11][12][13]. The fact that PLM was minimum from 38 to 94 h (this parameter did not exceed 10% on average) attests to a beginning of a new wave of PLM related to S phase of the second mitotic cycle.…”

“…The interest to these studies is determined by the fact that S-period, normally, includes two phases: S 1 and S 2 separated by an interval without DNA synthesis [7][8][9][10]. It is worthy of note that DNA replicated in the early S phase (S 1 phase) is enriched with G-C pairs and DNA synthesized at the end of (S 2 phase) is enriched with A-T pairs.…”