Amount Of Thymine Dimers Research Articles

Effects of enhanced UV-B radiation on hydroxycinnamic acid derivatives extracted from different cell compartments in the aquatic liverwort Jungermannia exsertifolia subsp. cordifolia

We examined the responses of ultraviolet-absorbing compounds (UVAC) to enhanced UV-B radiation in the aquatic liverwort Jungermannia exsertifolia subsp. cordifolia for 31 days under laboratory conditions. Samples were exposed to three radiation regimes: P (only photosynthetic radiation), PA (photosynthetic + UV-A radiation) and PAB (photosynthetic + UV-A + UV-B radiation). We measured both the bulk UV absorbance of the methanolic extracts and the levels of individual UVAC. In both cases, the methanol-soluble and the methanol-insoluble, alkali-extractable cell wall-bound fractions were analyzed. The bulk UV absorbance of the soluble fraction was higher than that of the cell wall-bound fraction. The bulk UV absorbances of both fractions increased under enhanced UV-B (PAB regime). Five different hydroxycinnamic acid (HCA) derivatives were found in the soluble fraction and two additional ones in the cell wall-bound fraction, among which only p-coumaroylmalic acid in the soluble fraction and p-coumaric acid in the cell wall-bound fraction increased under enhanced UV-B. The maximum quantum yield of PSII (F(v) /F(m)) decreased and DNA damage (amount of thymine dimers) strongly increased under enhanced UV-B, showing UV-B-induced damage. We conclude that methanol-soluble and cell wall-bound fractions of the liverwort studied have different UVAC, and each individual compound may respond in a different way to UV-B radiation. Thus, the analysis of individual UVAC in both the methanol-soluble and cell wall-bound fractions is advisable to better evaluate the protection mechanisms of liverworts against UV-B radiation. In particular, p-coumaric acid and p-coumaroylmalic acid seem to be especially UV-B responsive and merit further investigation.

Effects of UV radiation on DNA photodamage and production in bacterioplankton in the coastal Caribbean Sea

This study focuses on the effects of ultraviolet radiation (UVR) on bacterioplankton. The effect of different parts of the sunlight spectrum on the leucine and thymidine incorporation and on the induction of DNA damage in natural bacterial populations in the coastal Caribbean Sea off Curacao were investigated. DNA photodamage in microorganisms and biodosimeters was quantified by the number of cyclobutane dimers (thymine dimers). Increasing DNA damage during the day was found when incubated in full surface solar radiation. When UVBR was excluded no DNA damage was observed, indicating that thymine dimers were only formed by WE radiation. The amount of thymine dimers in the >0.8 mu m fraction was only one-third of the amount of induced thymine dimers in the

In Situ Molecular Dosimetry and Tumor Risk: UV‐lnduced DNA Damage and Tumor Latency Time‡

In UV carcinogenesis there is a fundamental chain of causal events from UV-induced DNA damage through mutations up to tumor formation: each of the early events should be predictive of the ultimate tumor risk. Instead of the UV surface exposure, the in situ load of DNA damage should be a more direct measure of the carcinogenicity. To explore this further we measured cyclobutane thymine dimer loads of epidermal cell suspensions from chronically UV-exposed hairless SKH-1 mice; skin samples were taken after various time periods under different daily exposures. Although the average load per cell decreased in the course of time due to dilution of damage in an increasing epidermal hyperplasia, the amount of thymine dimers in a column of epidermis (i.e. per mm2 of skin area) became stationary, and this amount increased with higher daily exposure. The median tumor latency time, t50, is inversely related to this stationary load. Extrapolation of a fitted relationship would imply a t50 between 450 and 1430 days for spontaneous skin carcinomas. The present data suggest that the skin strives to maintain a maximum level of tolerable DNA damage by lowering the average genotoxic load in vital cells in a hyperplastic reaction: pseudo-repair by dilution. This would also explain the strong hyperplastic reactions in DNA repair-deficient mouse strains. An understanding of these short-term adaptive reactions can refine our assessments of skin cancer risks in humans.

Establishment of a monoclonal antibody recognizing cyclobutane-type thymine dimers in DNA: a comparative study with 64M-1 antibody specific for (6-4) photoproducts

We obtained a monoclonal antibody (TDM-1) binding to 313-nm UV-irradiated DNA in the presence of acetophenone. The binding of TDM-1 to 254-nm UV-irradiated DNA was not reduced with the subsequent irradiation of 313-nm UV. Furthermore, the treatment of UV-irradiated DNA with photolyase from E. coli and visible light exposure reduced both the antibody binding and the amount of thymine dimers in the DNA. A competitive inhibition assay revealed that the binding of TDM-1 to UV-irradiated DNA was inhibited with photolyase, but not with 64M-1 antibody specific for (6-4)photoproducts. These results suggest that TDM-1 antibody recognizes cyclobutane-type thymine dimers in DNA.Using TDM-1 and 64M-1 antibodies, we differentially measured each type of damage in DNA extracted from UV-irradiated mammalian cells. Repair experiments confirm that thymine dimers are excised from UV-irradiated cellular DNA more slowly than (6-4)photoproducts, and that the excision rates of thymine dimers and (6-4)photoproducts are lower in mouse NIH3T3 cells than in human cells.

PHOTOREVERSIBILITY OF UV‐INDUCED THYMINE DIMERS AND ABNORMAL MORPHOGENESIS IN SEA‐URCHIN EMBRYOS

Abstract— Irradiation of synchronously dividing 16‐cell embryos of a sea‐urchin (Hemicentrotus pul‐cherrimus) with 200 J m−2 of UV light (254 nm) resulted in the complete inhibition of normal pluteus‐larva formation when the embryos were cultured in the dark after UV‐irradiation. Illumination of the UV‐irradiated embryos with visible light (11 W m−2) for 1 h immediately after the UV‐irradiation reversed the abnormal morphogenesis. Measurement of thymine dimers indicates that the degree of UV‐induced abnormal morphogenesis is greatly correlated with the amount of thymine dimers in the DNA of the embryos. The degree of the photoreversal decreased with an increase in the interval between UV‐irradiation and exposure to visible light. Visible light was ineffective as to the reversibility of both thymine dimers and the abnormal morphogenesis at 60 min after the UV‐irradiation, when the UV‐irradiated 16‐cell embryos entered the next cell cycle.

Photoreactivation and Excision Repair of Thymine Dimers in Ultraviolet-Irradiated Cultured Fish Cells

It was confirmed by colony-formation assays that cultured fish cells (CAF-MM1) are more sensitive to ultraviolet light (uv) than mammalian cells (mouse L cells). To study the high sensitivity of the fish cells, direct assay of thymine dimers was made by two-dimensional paper chromatography. The ratio of thymine dimers to thymine (TT/T) immediately after uv irradiation was proportional to uv dose and was 0.04% per 10 J/m/sup 2/ of uv. Similar values were also obtained in the mouse L cells used for comparison. When CAF-MM1 cells were incubated in the dark after uv irradiation, the value of TT/T did not change for up to 48 hr; that is, excision of dimers could not be detected. Visible light illumination immediately after uv irradiation reduced the amount of thymine dimers and increased the cell survival of CAF-MM1 cells. The results indicated a close relation between photoreactivation of dimers and the fraction of cells surviving. About half the thymine dimers could be photoreactivated upon exposure to visible light immediately after uv irradiation, but only 18% after 24 hr.

Excision of thymine dimers from the DNA of UV-irradiated plant seedlings

The kinetics of in vitro and in vivo thymine dimerization of grass pea ( Lathyrus sativa L.) DNA have been studied. The results showed that the amount of thymine dimers in isolated DNA was two fold higher than in irradiated seedlings. Pyrimidine dimers were excised from the DNA during the incubation of the UV-irradiated seedlings. Excision occurred within the first 6 hr of incubation in the dark. Similar proportions of dimers disappeared during photoreactivation. The decrease in the amount of thymine dimers in DNA was accompanied by their accumulation in the acid-soluble fraction. The enhanced incorporation of labeled thymidine into DNA after UV-irradiation in the presence of hydroxyurea indicates the possibility of unscheduled synthesis in the course of DNA repair after UV-irradiation of seedlings.

Analyses of differential sensitivities of synchronized hela S3 cells to radiations and chemical carcinogen during the cell cycle: (II) Ultraviolet light

UV-induction of thymine dimers in cellular DNA and their excision during different phases of the cell cycle of HeLa S3 cells were studied. Induction of thymine dimers was higher in the mitotic phase and the middle of the S phase than in the G 1 phase and from the late S phase to the early G 2 phase which are rather insensitive to UV. However, there is no significant difference in excision rate of UV-induced thymine dimers from the irradiated cells through the cell cycle. These findings indicate that the cyclic variation of UV-survivals during the cell cycle may be due to differences in the amount of thymine dimers in cellular DNA induced by UV-irradiation.

CHANGE IN THE BASE COMPOSITION OF MESSENGER RNA OF ESCHERICHIA COLI BY ULTRAVIOLET IRRADIATION AND ITS RECOVERY

Abstract— The base composition of messenger RNA in Escherichia coli B/r and B8–1 irradiated with ultraviolet (u.v.) light has been examined. The experimental results are as follows: (1) the synthesis of rapidly labeled RNA does not stop in ultraviolet irradiated bacteria. (2) The rapidly labeled RNA in irradiated cells shows a change in base composition corresponding to the formation of pyrimidine dimers in DNA molecules. The mole per cent of adenine component is increased with ultraviolet dose. The ratio of purine/pyrimidine becomes larger and the GC content smaller. (3) The base composition of the rapidly labeled RNA in irradiated bacteria reversed to that in unirradiated cells, when the irradiated cells were reactivated by experimental procedures for photoreactivation or dark reactivation. The reversion in the base composition corresponds well to the decrease in the amount of thymine dimers in DNA molecules. (4) The mechanism of the change in the base composition of rapidly labeled RNA caused by ultraviolet irradiation is discussed.