Griffiths, T. Daniel
M.S. (Master of Science)
Department of Biological Sciences
Cells--Effect of radiation on||DNA||Ultraviolet radiation--Physiological effect
There has been great debate concerning the roles of the pyrimidine(5-6)pyrimidine and pyrimidine(6- 4)pyrimidone lesions. Previous work in this area, with Chinese hamster ovary (CHO) cells, has shown the (6-4) lesion to be more important than the (5-6) lesion in affecting cell survival, DNA synthesis, mutation and sister chromatid exchange (SCE) induction. We used CHO cells AA8 (repair-proficient in removing both lesions), UV61 (removes only the (6-4) and not the (5-6) lesions) and UV5 (removes neither lesion). Cell survival studies showed UV5 cells were more sensitive to ultraviolet light (UV) than UV61 cells. DNA synthesis studies showed a fluence dependent effect. The (6-4) lesion played a greater role than the (5-6) in decreasing DNA synthesis at 2.5 J/m². At 5 and 10 J/m², the (5-6) lesion played a greater role in inhibiting DNA synthesis than seen at 2.5 J/m². DNA chain elongation was studied by using DNA fiber autoradiography. Our results indicated the (5-6) lesion did not form long-term blocks to DNA chain elongation. DNA fiber autoradiography was also used to detect and measure the activation of alternative sites of initiation. The (5-6) lesion did activate alternative sites. This activation remained longer than that seen in AA8 cells but was removed by 5 hrs. SCE studies showed the (6-4) lesion played a major role in SCE induction. Mutation results indicated the (5-6) lesion caused mutations more frequently than the (6-4), especially at fluences less than 1 J/m². The (6-4) lesion appears to play a greater role than the (5-6) lesion in cell survival, DNA synthesis, DNA replication (initiation and elongation) and SCE induction. The (6-4) lesion does play a role in mutation but the (5-6) lesion causes most of the increases seen in mutation frequency.
Taft, Sharon A., "Elucidation of the relative roles of the (5-6) and (6-4) UV-induced lesions in CHO cell survival, DNA synthesis and mutation" (1990). Graduate Research Theses & Dissertations. 2848.
v, 117 pages
Northern Illinois University
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