Doses Of Ultraviolet Light Research Articles

Directly photocrosslinked nucleotides joining transfer RNA to aminoacyl-tRNA synthetase in methionine and tyrosine systems

We have used ultraviolet photocrosslinking and 32P post-labeling to help define the contact surface between transfer RNAs and aminoacyl-tRNA synthetases for the methionine and tyrosine systems. Photocrosslinking between tRNAs and synthetases is shown to occur only in cognate complexes. The increased sensitivity of our procedures reduces the amounts of interacting macromolecules and permits lower ultraviolet light doses, thereby minimizing radiation damage. These procedures have detected crosslinks only within the 3′-terminal RNase T 1 fragments in yeast tRNA i Met and Escherichia coli tRNA 2 Tyr; and although the photoadducts were unstable, we have identified the crosslinked nucleotides. These crosslinks occur at positions C74 and A76 in yeast tRNA i Met and position U64 in E. coli tRNA 1&2 Tyr (conventional tRNA numbering system of Gauss & Sprinzl, 1981). This work demonstrates that even labile photocrosslinks can be exploited for mapping crosslinked nucleotides.

Acute Effects of Ultraviolet Light B on Morphology and Epidermal Cell Kinetics in Human Skin Transplanted to Nude Mice

Grafts of human skin on nude mice were irradiated with varying doses of ultraviolet light B and at various intervals were subjected to histological examination and determination of the epidermal 3H-thymidine labelling index. The studies showed that the human skin in the foreign milieu of the nude mouse retained its ability to respond to phototoxic damage. The findings suggest that the nude mouse/human skin model could be a valuable tool in human photodermatological research.

Evidence that DNA excision-repair in xeroderma pigmentosum group A is limited but biologically significant

The loss of pyrimidine dimers in nondividing populations of an excision-repair deficient xeroderma pigmentosum group A strain (XP12BE) was measured throughout long periods (up to 5 months) following exposure to low doses of ultraviolet light (UV, 254 nm) using a UV endonuclease-alkaline sedimentation assay. Excision of about 90% of the dimers induced by 1 J/m 2 occured during the first 50 days. The rate curve has some similarities with that of normal excision-repair proficient cultures that may not be coincidental. Rate curves for both XP12BE and normal cultures are characterized by a fast and slow component, with both rate constants for the XP12BE cultures (0.15 day −1 and 0.025 day −1) a factor of 10 smaller than those observed for the respective components of normal cell cultures. The slow components for both XP12BE and normal cultures extrapolate to about 30% of the initial number of dimers. No further excision was detected throughout an additional 90-day period even though the cultures were capable of excision-repair of other newly-introduced pyrimidine dimers. We conclude that nondividing XP12BE cells in addition to having a slower repair rate, cannot repair some of the UV-induced DNA damage. The repair in XP12BE is shown to have biological significance as detected by a cell-survival assay and dose-fractionation techniques. Nondividing XP12BE cells are more resistant to UV when irradiated chronically than when irradiated acutely with the same total dose.

Ethionine abolishes mutagenesis by 9-aminoacridine (but not by 2-aminopurine) in Salmonella plate tests

Ethionine, the ethyl analogue of methionine, appears to be non-mutagenic in the 'Ames' series of bacterial tester strains (McCann et al., 1975), weakly mutagenic to some fungi (Lewis and Tarrant, 1971; Talmud and Lewis, 1974), and carcinogenic to rats after prolonged feeding (Farber, 1963). More recently, ethionine has been reported to block certain 'SOS' functions in a t i fmu tan t of Escherichia coli following thermal treatments (Weisner and Troll, 1981). Such SOS functions, including prophage induction, filamentous growth and recA +-dependent mutagenesis, are normally switched on in t i fmu tan t s following a temperature shift from 37 ° to 42 ° (Witkin, 1976). Weisner and Troll (1981) found that thermal induction of prophage lambda in a t i f m u t a n t of E. coli did not occur in the presence of 10 mM ethionine. Moreover, the increased mutation response normally observed in t i fcells irradiated with a low dose of ultraviolet light, and then raised to 42 ° (see Witkin, 1976 for details) is abolished by 10 mM ethionine. To determine whether the effects of ethionine on bacterial mutagenesis were restricted to events associated with thermal induction in t i f strains, we initiated a study of the effects of ethionine on chemical mutagenesis in t i f + strains of Salmonella typhimurium. We were particularly interested in possible effects on mutagenesis by 2-aminopurine and 9-aminoacridine, since we have shown that the mutagenic effects of these agents are largely independent of the recA + gene product in S. typhimurium (results to be published elsewhere). In addition, we were interested in the possibility that ethionine might act as an inhibitor of certain DNA methylation reactions, including the methylation of adenine residues which is associated with the product of the E. coli dam ÷ gene and plays an important part in mismatch repair (Marinus, 1973; Glickman et al., 1978). We reasoned that inhibition of a gene product equivalent to the dam + gene product by ethionine in S.

Improvement of the hairless mouse screening model for antipsoriatic drugs.

SUMMARY The hairless mouse screening model for antipsoriatic drugs was improved by investigating the effects of critical variables on the rate of ultraviolet light-induced epidermal DNA synthesis. The variables investigated were diurnal variation, ultraviolet light dose, time course and ambient temperature. From these studies a set of experimental conditions was developed that resulted in the lowest rate of DNA synthesis in non-irradiated epidermis and the highest rate in irradiated epidermis, thereby significantly increasing the power of the assay.

Rapid complementation method for classifying excision repair-defective xeroderma pigmentosum cell strains

A rapid method has been developed that permits demonstration of complementation between different cell strains from ultraviolet-sensitive xeroderma pigmentosum patients. Combining polyethylene glycol-mediated cell fusion with low doses of ultraviolet light to eliminate unfused sensitive cells, the method permits assignment of cell strains to complementation groups by visual inspection, avoiding use of laborious methods involving autoradiography. This method can be augmented by measuring DNA repair synthesis, which shows large quantitative differences between fusions that result in complementation and those that do not.

Constant low-dose ultraviolet light therapy for psoriasis

In a bilateral comparison study, symmetric plaques of psoriasis were used to compare the effects of a constant low dose (3 minutes, 30 seconds) of ultraviolet light therapy to the standard increasing ultraviolet light dose. The low constant dose of ultraviolet light was as efficacious in clearing psoriasis lesions as the higher increasing dose.

The epidermal melanocyte population in the skin of ultraviolet-irradiated crested newt.

The response of the epidermal melanocyte population to repeated ultraviolet (UV) exposure (wavelength spectrum 275-350 nm) has been investigated in the crested newt, Triturus cristatus carnifex. The effects of different doses of UV light were studied. The animals were killed 7 months after the first UV exposure. Only a slight decrease in the number of pigment cells was found after 85 sequential irradiations with a total dose of 1.3 x 10(5) J/m2, whereas striking decreases were observed when the same total dose was fractionated into 14 exposures or when a double dose was given in 57 exposures. The relationship between the square roots of the epidermal melanocyte densities and single doses appeared to be roughly linear, at least over the range of doses administered. The main factor in melanocyte damage seemed to be the single dose of irradiation rather than the cumulative dose administered. Decreased melanin content of the keratinocytes was observed in most irradiated animals.

Effects of radiation on the survival of excision-defective cells from Drosophila melanogaster.

The effect of various doses of ultraviolet light and ionizing radiation on the survival of excision-defective Drosophila cells has been determined by cloning treated and untreated cells in agarose. Although excision-defective cells survive moderate amounts of DNA damage, they display a severe hypersensitivity to both types of radiation relative to excision-proficient cells. Exposure of ultraviolet-irradiated cells to fluorescent light results in a reduction of the density of pyrimidine dimers in cellular DNA and a 10-to 20-fold increase in survival. Parallel analysis of dimer density and survival, however, suggests that much of the lethal effect of ultraviolet light is due to nondimer damage. Cell proliferation was monitored in both excision-proficient and excision-defective cells exposed to doses of ultraviolet light that reduced survival by 90%. Under these conditions excision-proficient cells displayed exponential growth whereas excision-defective cells exhibited no cell proliferation for 12 days.

Induction and Characterization of Chlorate-resistant Strains of Rosa damascena Cultured Cells

The sensitivity of Rosa damascena cultured cells to chlorate was measured by plating samples of suspensions in agar containing NaClO(3). This sensitivity depended on the age of the cultures that were plated. Chlorate-resistant colonies isolated from 5- to 7-day cultures retained their resistance through many generations of growth in medium lacking NaClO(3); they also retained resistance when mixed with sensitive cells. Treating cell aggregates with ultraviolet (UV) light (254 nanometers), or UV light (360 nanometers) in the presence of 4'-methoxymethyltrioxsalen, increased the proportion that was resistant to NaClO(3). However, the amount of increase was low (three times) and required very specific doses of UV light. The UV treatments did not select for chlorate-resistant cells over chlorate-sensitive cells. The data suggested that UV had induced mutations leading to chlorate resistance. Approximately 15% of the resistant strains did not grow on medium containing nitrate as the sole nitrogen source. These strains lacked ability to reduce chlorate to chlorite. This observation supports the current idea that chlorate toxicity depends on the activity of nitrate reductase. Approximately 85% of the resistant strains grew on medium containing nitrate as the sole nitrogen source. These strains lost catalase activity following chlorate treatment, indicating that they took up and reduced chlorate. These strains have a mechanism for tolerating chlorate and its reduction products, rather than avoiding them.

Postreplication repair in Saccharomyces cerevisiae.

Postreplication events in logarithmically growing excision-defective mutants of Saccharomyces cerevisiae were examined after low doses of ultraviolet light (2 to 4 J/m2). Pulse-labeled deoxyribonucleic acid had interruptions, and when the cells were "chased," the interruptions were no longer detected. Since the loss of interruptions was not associated with an exchange of pyrimidine dimers at a detection level of 10 to 20% of the induced dimers, we concluded that postreplication repair in excision-defective mutants (or leaky mutants) does not involve molecular recombination. Pyrimidine dimers were assayed by utilizing the ultraviolet-endonuclease activity in extracts of Micrococcus luteus and newly developed alkaline sucrose gradient techniques, which yielded chromosomal-size deoxyribonucleic acid after treatment of irradiated cells.

Aphidicolin inhibits repair of DNA in UV-irradiated human fibroblasts

Aphidicolin, a specific inhibitor of DNA polymerase α, is shown to inhibit DNA repair in human diploid fibroblasts. Although aphidicolin has no apparent effect on the DNA of unirradiated cells, it causes a large number of strand breaks to accumulate in UV-irradiated cellular DNA. The number of breaks is the same as the number observed following a similar dose of ultraviolet light when cells are treated with arabinofuranosyl cytosine (araC) and hydroxyurea (HU), known inhibitors of repair. Moreover, two-dimensional paper chromatography shows that aphidicolin completely blocks removal of pyrimidine dimers. These observations are discussed in light of the proposed roles of DNA polymerases α β in DNA replication and repair and the action of aphidicolin on polymerase α.

The in vivo formation and repair of DNA adducts from 1'-hydroxysafrole.

1'-Hydroxysafrole is a proximate carcinogenic metabolite of the naturally occurring hepatocarcinogen safrole. Comparison by high-performance liquid chromatography of the nucleoside adducts obtained from hepatic DNA of adult female mice treated with [2',3'-3H]1'-hydroxysafrole with those formed by reaction of deoxyribonucleosides with electrophilic derivatives of 1'-hydroxysafrole indicated that the four in vivo adducts studied were derived from an ester of 1'-hydroxysafrole. Three of the four adducts comigrated with products of the reaction of 1'-acetoxysafrole with deoxyguanosine, whereas the fourth adduct comigrated with the major reaction product of the ester with deoxyadenosine. Analysis of the three deoxyguanosine adducts indicated that all three involve substitution on the 2-amino group of guanine. A sample of ther major adduct prepared from deoxyguanylic acid has been characterized from its NMR spectrum as N2-(trans-isosafrol-3'-yl)-deoxyguanosine, and the deoxyadenosine adduct has been similarly characterized as N6-(trans-isosafrol-3'-yl)-deoxyadenosine. Repair replication was measured in cultured human T98G cells exposed to 1'-acetoxysafrole using the combined 5-bromodeoxyuridine density label and radioisotopic label method. At a concentration of 1 mM 1'-acetoxysafrole, the amount of repair synthesis approached maximum values only about 15% of those obtained after saturating doses of ultraviolet light. Repair patch size distribution was found to be similar in cells treated with ultraviolet light or 1'-acetoxysafrole as determined by the density of repair-labeled DNA relative to that of parental DNA.

Effect of caffeine on DNA synthesis in irradiated and unirradiated mammalian cells

Caffeine increased the availability of replication origins, and consequently the number of growing points, in the DNA of Chinese hamster V79 and human (HeLa) cells. Caffeine also prevented the inhibition of replicon initiation normally caused by X-radiation and exposure to low doses of ultraviolet light. When caffeine was removed from the medium after irradiation, replicon initiation was inhibited. Caffeine also reversed the inhibition of replicon initiation caused by novobiocin, which is not a DNA-damaging agent. Because caffeine increases the number of growing points, it also partially reversed the inhibition of total DNA synthesis induced by hydroxyurea. It is proposed that caffeine alters the conformation of intracellular chromatin in such a way that the conformation usually induced by DNA-damaging agents is prevented.

Double mutations induced in Escherichia coli by ultraviolet light

Double mutations to azide resistance and to bacteriophage T5 resistance of genes separated by more than 50 kilobases were induced in Escherichia coli WP2s in chemostat cultures by exposure to a single low dose of ultraviolet light. Frequencies of induced double mutations were three orders of magnitude greater than would be predicted by chance. Reversions from azide resistance and phage resistance occurred independently, showing that that the double mutation was not due to pleiotropic effects of a single gene mutation. These results support earlier findings which show that low doses of ultraviolet light induce multiple gene mutations in Bacillus subtilis over a similarly broad range.

Factors Affecting Sperm Motility. III. Influence of Visible Light and Other Electromagnetic Radiations on Human Sperm Velocity and Survival

Specimens of semen from fertile and infertile patients were exposed to different electromagnetic radiations, including visible light, ultraviolet (UV) light, x-rays, and high-frequency radio waves. Sperm motility was analyzed before, during, and after irradiation by the multiple exposure photography (MEP) method. No significant difference was found between controls and specimens exposed to various doses of visible and UV light and x-rays either immediately or several hours after exposure. In contrast to spermatozoa of other species that were reported to be adversely affected by visible and UV light and x-rays, human spermatozoa seem to be highly resistant to similar doses of these radiations. A deleterious influence was observed when high-frequency radio waves were applied to human spermatozoa. This may be attributed to an intracellular diathermic effect. The informative value of this study in relation to routine semen analyses and experimental studies in the physiology and comparative anatomy of spermatozoa is discussed.

DNA repair synthesis in HeLa cell lysate

In order to study the mechanism of DNA repair, we established an in vitro system for repair (unscheduled) DNA synthesis. HeLa cells synchronized at G2-G1 phase were irradiated with ultraviolet light in the presence of two DNA replication inhibitors, hydroxyurea and 1-β- d-arabinofuranosyl cytosine (araCyt), to reduce the replicative DNA synthesis as much as possible. Hypotonic treatment of the cells was followed by gentle homogenization, and the resulting cell lysate was incubated with [ 3H]dTTP. The lysate system required all four dXTPs and Mg 2+, but required no ATP. The incorporation of [ 3H]dTTP was dependent on the dose of ultraviolet light, was linear for 2 min, and reached the maximum at 5 min. The presence of hydroxyurea and araCyt during in vivo incubation was necessary for in vitro DNA synthesis. Accumulation of single-strand breaks was observed under these conditions, and this could explain the very high incorporation of [ 3H]dTTP in this system.

Inactivation of prophage in ultraviolet-irradiated Escherichia coli: dependence on recA gene activity

The fate of the prophage part of the lysogenic chromosome was followed in the course of post-ultraviolet incubation. For this purpose, lambda cI857 ind prophage, which can be induced by heat but not by ultraviolet light, was used. The prophage, intially more resistant than its repair-proficient host cell, was rapidly inactivated. This inactivation was not caused by the impaired capacity of irradiated cells to support growth of the phage. Over the entire dose range tested, little, if any, sensitivity difference between the host and the prophage was found at the end of cell division delay. Rapid inactivation of the prophage was also observed in uvr cells after small doses of ultraviolet light. The same small doses did not cause inactivation in lysogens carrying a mutation in the gene recA. This suggests that the functional gene recA is required for inactivation of the prophage part of the lysogenic chromosome.

UVL Induced Changes in Calcium Absorption and Excretion and in Serum Vit D3 Levels measured in Black-skinned and Caucasian Males

AbstractWith the evident increase in osteolytic disease, especially in black-skinned urban communities, it has become necessary to attempt to define and measure dietetic and environmental factors contributing to this increase. This paper describes and measures calcium absorption and excretion and serum hydroxy-cholecalciferol (Vit D3) levels in both black-skinned and caucasian controls exposed to similar doses of ultra-violet light. It is concluded that there is a significant difference in response to UVL stimulus between the two groups to the detriment of the blackskinned population.

Functionally distinct classes of complex phosphorus compounds in lake water1

Complex phosphorus compounds were classified functionally according to the manner by which orthophosphate was released. Filtrable phosphorus compounds in two eutrophic lakes (East and West Twin lakes) and a humic bog (Crazy Eddie Bog) in northeastern Ohio were fractionated by anion‐exchange and gel‐filtration chromatography. Fractions were analyzed for soluble reactive phosphorus and total dissolved phosphorus; absorbance at 400 nm was used as a measure of filtrable “yellow acids.” The eutrophic lakes contained numerous low molecular weight compounds which were resistant to low‐dose ultraviolet irradiation but readily released orthophosphate upon treatment with alkaline phosphatase. Filtrable phosphorus compounds of the humic bog were predominantly high molecular weight, cochromatographed with the yellow acids in each fractionation procedure, and resisted enzyme hydrolysis, but released orthophosphate upon irradiation with low doses of ultraviolet light.