Enzymic excision of ultraviolet-induced cytosine hydrates from left-handed DNA
- Temple Univ., Philadelphia, PA (United States)
Ultraviolet irradiation of DNA produces a variety of pyrimidine modifications. These include cytosine hydrate (5,6-dihydro-6-hydroxycytosine), released as a free base by E. coli endonuclease III. The enzymic excision of cytosine hydrate by this purified enzyme was investigated by assaying release of labeled photoproduct from DNA into the ethanol-soluble fraction. Ultraviolet-irradiated poly(dG-dC):poly(dG-dC), radio-labeled in cytosines, was used as substrate. Shifts between the right-handed B-conformation and the left-handed Z-conformation were effected by heating the polymer in the presence of either Ni(II) or Co(II). Conformational states were determined by ultraviolet circular dichroism. Rates of enzymic cytosine hydrate release did not differ between the different substrate conformations, B-DNA and Z-DNA. Irradiation of left-handed poly(dG-dC):poly(dG-dC) resulted in cytosine hydrate formation. Therefore, neither formation nor enzymic excision of ultraviolet-induced cytosine hydrates are substantially affected by the DNA conformational state. Cytosine hydrates are most likely to occur in alternating purine:pyrimidine sequences. Such segments can adopt the Z-conformation as a result of reactions with chemical carcinogens, the presence of metal ions, or negative superhelicity. These results indicate repair of cytosine hydrates to be likely, regardless of the DNA conformational state.
- OSTI ID:
- 5679995
- Report Number(s):
- CONF-9004153--
- Journal Information:
- FASEB Journal (Federation of American Societies for Experimental Biology); (United States), Journal Name: FASEB Journal (Federation of American Societies for Experimental Biology); (United States) Vol. 4:3; ISSN 0892-6638; ISSN FAJOE
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
Cells
& Tissue Culture
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
AMINES
AZINES
BACTERIA
BIOLOGICAL EFFECTS
BIOLOGICAL RADIATION EFFECTS
BIOLOGICAL RECOVERY
BIOLOGICAL REPAIR
CYTOSINE
DNA
DNA REPAIR
DNA-ASE
ELECTROMAGNETIC RADIATION
ENDONUCLEASES
ENZYMES
ESCHERICHIA COLI
ESTERASES
EXCISION REPAIR
HETEROCYCLIC COMPOUNDS
HYDRATES
HYDROLASES
MICROORGANISMS
NUCLEIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
PHOSPHODIESTERASES
PROTEINS
PYRIMIDINES
RADIATION EFFECTS
RADIATIONS
RECOVERY
REPAIR
ULTRAVIOLET RADIATION