Excision-repair of $gamma$-ray damaged thymine in bacterial and mammalian systems
- ed.
The selective excision of products of the 5,6-dihydroxy-dihydrothymine type (t') for $gamma$-irradiated or OsO$sub 4$-oxidized DNA or synthetic poly [d(A-T)] was observed with crude extracts of Escherichia coli and isolated nuclei from human carcinoma HeLa S-3 cells and Chinese hamster ovary cells. The results with E. coli extracts allow the following conclusion: The uvrA-gene product is not required for t' excision; radiation-induced strand breakage is not required for product excision; experiments with extracts of E. coli polAexl showed that the 5' $Yields$ 3' exonuclease associated with polymerase I is responsible for the removal of t'; experiments with extracts of E. coli endo I lig 4 and the ligase inhibitor nicotinamide mononucleotide showed that polynucleotide ligase accomplishes the last strand resealing step in the excision-repair of t'. Isolated nuclei from HeLa and Chinese hamster ovary cells possess the necessary enzymes for the selective excision of t' from $gamma$-irradiated or osmium tetroxide oxidized DNA. Approximately 25 to 35 percent of the products were removed from DNA within 60 min. Unspecific DNA degradation was very low. Radiation-induced strand breakage is not required for product removal. (auth)
- Research Organization:
- Univ. of Florida, Gainesville
- NSA Number:
- NSA-33-012260
- OSTI ID:
- 4126324
- Country of Publication:
- United States
- Language:
- English
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