RANDOM DISTRIBUTION OF HIGHLY REPETITIVE AND INTERMEDIATE FREQUENCY MOUSE L-929 CELL DNA SEQUENCES SYNTHESIZED AFTER UV LIGHT EXPOSURE |
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Authors: | Martin L Meltz Nancy Jo Whittam William H Thornburg |
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Institution: | Southwest Foundation for Research and Education, P.O. Box 28147, San Antonio, TX 78284, U.S.A. |
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Abstract: | Abstract— The DNA precursor 3H-thymidine incorporation rate (dpm/pg DNA) in mouse L-929 cells decreases immediately after exposure to UV light. This decrease is initially dose dependent, but at exposures greater than 22.5 J/m2 appears to be radio-resistant. This was not explained by measurements of uptake of 3H-thymidine into the acid soluble pool (dpm/pg DNA). The radio-resistant incorporation amounted to approximately 35% of the control rate. DNA reassociation ("C0T") studies were performed with DNA labeled with 3H-thymidine immediately after exposure of L-929 cells with a dose of UV resulting in radio-resistant incorporation to determine whether this radio-resistant incorporation was occurring in sequences of a particular repetitious frequency. These studies, performed in the highly repetitive to intermediate range, showed that the radio-resistant incorporation was occurring in DNA of all classes of repetitious frequency. DNA synthesized at different times after UV exposure, during the period when post-replication repair can occur, was similarly labeled for short intervals and isolated. The DNA reassociation studies showed that this DNA synthesis was also of all classes of repetitious frequency. |
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