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Using Hayflick's model, ultraviolet (UV)-induced unscheduled DNA synthesis was compared in cells at a low, middle and high population doubling level (PDL). Concomitant DNA replication was prevented by arresting all cultures in the G1 phase by lowering the serum concentration. After UV-irradiation cells at a high PDL incorporated 1.5-2 times more [3H]thymidine into DNA than cells at a low and middle PDL. These findings seem to indicate that the repair capacity of cells at a high PDL is more than those of cells at low and middle PDL. Alternatively, the higher incorporation might be explained by a difference in the pool sizes of precursors of cells at different PDL. These possibilities were examined by adding fluorodeoxyuridine to the system to reduce de novo synthesis of deoxythymidine triphosphate (dTTP), and measuring the pool size of dTTP and the specific activity of [3H] dTTP in cells at different PDL. The results indicated that the increased incorporation in fact reflects increased unscheduled DNA synthesis in cells at a high PDL.
N Hasegawa, and
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October 1978,
Mechanisms of ageing and development,
N Hasegawa, and
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April 1984,
Mutation research,
N Hasegawa, and
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April 1981,
Cell biology international reports,
N Hasegawa, and
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October 1982,
Photochemistry and photobiology,
N Hasegawa, and
F Hanaoka, and
M Yamada
March 1987,
Experimental cell research,
N Hasegawa, and
F Hanaoka, and
M Yamada
January 1981,
Journal of supramolecular structure and cellular biochemistry,
N Hasegawa, and
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M Yamada
January 1992,
Experimental gerontology,
N Hasegawa, and
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M Yamada
January 1990,
Basic life sciences,
N Hasegawa, and
F Hanaoka, and
M Yamada
December 1971,
Mutation research,
N Hasegawa, and
F Hanaoka, and
M Yamada
January 1983,
IARC scientific publications,
