Endonucleolytic Incision of Uvb‐irradiated Dna

Abstract

Abstract. Ultraviolet irradiation of DNA produces a variety of pyrimidine damage. In addition to the well‐known photoproducts, pyrimidine dimers and 6‐4′(pyrimidin‐2'one)pyrimidines, DNA sequence analysis has shown that E. coli endonuclease III incises broad‐spectrum UV‐irradiated DNA at cytosines. The same enzyme incises DNA oxidized by osmium tetroxide at damaged thymines. The wavelength dependence of endonuclease III incision of irradiated DNA was examined. DNA substrates were irradiated by monochromatic light ranging from 250 to 320 nm. Maximal enzymic cleavage was obtained with substrates irradiated by wavelengths between 265 and 285 nm, with peak activity against DNA irradiated at 280 nm. Therefore, these photoproducts are optimally formed at biologically significant wavelengths and may be involved in actinic carcinogenesis.

Wavelength Dependence of Dna Incision by a Human Ultraviolet Endonuclease

“…The peak of enzyme-sensitive sites in the irradiated superhelical substrate was produed at wavelengths between 270 and 295 nm. This wavelength dependence of DNA breakage by the human enzyme is virtually identical to that demonstrated for E. coli endonuclease 111 using the same assay (Weiss and Duker, 1987).…”

“…Both techniques used here show the wavelength dependence of substrate incision by the human endonuclease to correspond to that of E. coli endonuclease 111 (Weiss and Duker, 1987). Activities corresponding to these enzymes have been found in a wide variety of prokaryotic and eukaryotic cells.…”

“…precipitated with ethanol, and subjected to DNA sequencing reactions as previously described (Weiss el a / . , 1983; Weiss and Duker, 1987). The formation of endonuclease-sensitive sites in superhelical DNA was detected by the filter-binding assay according to Teebor and Brent (1981).…”

Molecular Mechanisms of Ultraviolet Radiation Carcinogenesis

“…Recent studies indicate that UV radiation also induces other non-dimer photoproducts such as (6-4) photoproducts (Haseltine, 1983;Mitchell and Nairn, 1989), cytosine photohydrates (Weiss and Duker, 1987;Doetsch et al, 1988), purine photoproducts (Gallagher and Duker, 1989). and singlestrand breaks in the DNA .…”

Nucleotide sequence of the xth gene of Escherichia coli K-12

“…Endonuclease III differs from exonuclease III in several respects. It cleaves on the 3' side of AP sites via a ,-elimination reaction (1); it has a glycosylase activity which releases ring-fragmented thymines (3,4,10,16) and a cytosine UV photoproduct (11); and it incises damaged DNA at cytosines (11,12,14,43,44) and guanines (12). Endonuclease IV cleaves phosphodiester bonds at AP sites to yield base-free deoxyribose 5-phosphate end groups (9); it can remove 3'-phosphoglycolates, 3'-phosphates, and 3'-unsaturated deoxyribose from DNA (9); and it can cleave DNA at apyrimidinic sites formed by neocarzinostatin which are refractory to clea'vage by exonuclease III (25).…”