The recovery of normal DNA replication kinetics in ultraviolet-irradiated Chinese hamster cells |
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Authors: | Raymond E. Meyn Margaret R. Kasschau Roger R. Hewitt |
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Affiliation: | 1. Department of Physics, The University of Texas System Cancer Center, M.D. Anderson Hospital and Tumor Institute, Houston, Texas 77030, U.S.A.;2. Department of Biology, The University of Texas System Cancer Center, M.D. Anderson Hospital and Tumor Institute, Houston, Texas 77030, U.S.A. |
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Abstract: | The kinetics of DNA replication were analyzed in the second S phase following UV irradiation of Chinese hamster ovary cells synchronized at the beginning of S phase. The cells were synchronized by treating cells selected in mitosis with hydroxyurea for 9 h. Following UV irradiation, the cells were allowed to progress until the next mitosis; at which time they were resynchronized at the beginning of the second S phase by the same procedure. The kinetics of DNA replication were determined by measuring the proportion of DNA which achieved hybrid buoyant density on CsCl density gradients as a function of the time of incubation in the presence of 5-bromodeoxyuridine.The results of these experiments showed that even though the rate of DNA replication is substantially depressed during the first S phase following UV irradiation with a fluence of 5 J/m2, the rate has recovered to the extent that it is indistinguishable from the unirradiated control by the time the cells have entered their second S phase. It was concluded from these observations that the lesions in DNA which caused the rate of DNA replication to be initially depressed during the first S phase have been either removed or modified such that they no longer are able to cause a reduction in the rate of DNA replication in the second S phase following UV irradiation. |
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