Showing papers on "Ultraviolet light published in 1970"

Mutants of diplococcus pneumoniae that lack deoxyribonucleases and other activities possibly pertinent to genetic transformation.

Abstract: Mutants of Diplococcus pneumoniae that lacked the two major deoxyribonucleases of the cell—one an endonuclease, the other an exonuclease preferentially active on native deoxyribonucleic acid (DNA)—were obtained. The development of a method for detecting mutant colonies, based on the binding of methyl green to DNA, facilitated isolation of the mutants. Neither enzyme was essential for growth of the cells, for repair of ultraviolet damage, or for any phase of DNA-mediated transformation. Residual deoxyribonuclease activity in the double mutant corresponded to an exonuclease, approximately one-fifth as active as the major exonuclease, that attacked native and denatured DNA equally well. This activity appeared to be associated with the DNA-polymerase enzyme. A mutant that apparently lacked a cell wall lytic enzyme was also fully transformable. A mutant strain that was four times more sensitive to ultraviolet light than the wild type also transformed normally. Recipient cells of this strain were deficient in the repair of ultraviolet-irradiated transforming DNA. Mutants were found which, unlike the wild type, integrated donor markers only with high efficiency, thereby indicating that a particular cellular component that is susceptible to loss by mutation, such as an enzyme, is responsible for low integration efficiency. Images

Adhesive Sealing of Pits and Fissures for Caries Prevention, With Use of Ultraviolet Light

Abstract: Complete protection against caries was obtained when tooth surfaces were shielded from exposure to the oral environment. Tests of a new adhesive material that hardens when exposed to ultraviolet light showed 100% caries protection after one year in 200 deciduous and permanent teeth. Forty-two percent of the matched contralateral control teeth developed caries. This simple preventive measure requires only a few minutes per tooth, and lends itself to use by the dental hygienist after routine prophylaxis.

Transient Acantholytic Dermatosis

Abstract: Six patients with an apparently unique, self-limited, primary acantholytic skin disease are described. The elementary lesions were pruritic, discrete, edematous papules or vesiculopapules which tended to appear first on the trunk, possibly as a Koebnerlike response to nonspecific irritation, such as ultraviolet light. The two youngest patients, aged 46 and 48, developed only localized manifestations which disappeared in a few weeks. The older patients, ranging from 56 to 74 years old, had disseminated eruptions which lasted several months. Although there was a strong histologic resemblance to Darier's disease in three cases, and to Hailey-Hailey's disease in the other three, clinical considerations seem to rule out both of these diagnoses. It is stressed that cytologic examination is most useful in recognizing the disease.

Inactivation of the Scrapie Agent by Near Monochromatic Ultraviolet Light

Abstract: SCRAPIE is a progressive degenerative disease of the central nervous system of sheep. Because the disease is transmitted by cell-free filtrates the agent has been classified as a virus, but its response to many chemical and physical treatments has long been known to differ from that of “conventional” viruses. The transmitting agent increases greatly in quantity in the animal host. In the terminal stages of the disease in mice, preparations from the brain must usually be diluted by a factor of 107–108 to give an average of one mean lethal dose per unit volume, whatever the original inoculum to the affected mouse has been. Haig and Clarke1, who used a substantial starting inoculum to follow the “growth” of the agent, showed an increase by a factor of 104 in the titre of the agent in mouse brain by the time the terminal stage was reached. But experiments with ionizing and ultraviolet radiations led Alper et al.2,3 to question whether the agent depended on replication of a nucleic acid moiety for proliferation, which was shown to occur also when the titre of the injected material had been reduced by irradiation in vitro4. The dose of ionizing radiation required to give an average of one inactivating event per infective unit was much larger, and the inferred “target volume” (molecular weight about 1.5 × 105, ref. 2) therefore much smaller, than for any virus; if the “target” were nucleic acid, this molecular weight would be too low to allow of sufficient coding information for replication. With ultraviolet irradiation at 254 nm, detectable inactivation required doses which were very large compared with those which inactivated even the most “resistant” entities whose function depended on the integrity of nucleic acid3,4. This suggested that the agent might be comparatively transparent to ultraviolet of wavelength in the “germicidal” region in which nucleic acids absorb most strongly.

Human chromosome damage by chemical agents.

Abstract: Two news items concerning the nation's health appeared last autumn. On October 18, 1969, Health, Education and Welfare Secretary Robert H. Finch announced a ban on cyclamate-containing foods because this artificial sweetening agent causes bladder cancer in rats. One week later, the presi­ dents of three baby food companies announced they would voluntarily dis­ continue the use of the flavor-enhancer monosodium glutamate (MSG) because it produced brain damage in newborn mice. The removal of these two food additives will change the dietary habits of millions of people. Agents which cause cancer or birth defects are easily recognized, even hy the layman, as dangerous. But what about agents which cause more subtle damage such as genetic mutation or chromosome breakage. Because changes in the genes and chromosomes do not usually produce an immediate health hazard, they may go undetected for a lifetime or even for several generations. Yet, the human gene pool can become insidiously polluted. This review concerns chemical agents which break chromosomes. Early in the writing of this article, it became apparent that a term was needed for the cumbersome phrase "chromosome-breaking agent." Already introduced into medical literature were such descriptive terms as carcinogen, leu­ kemogen, mutagen, and teratogen. The word "chromosomoclastogen" is suggested; the Greek word root "-clast" means to break, fracture, or frag­ ment. (Recall the terms osteoclast and iconoclast.) In this article, an abbre­ viated, more euphonious form, "clastogen" will be used. A number of physical, chemical, and biological agents are known to break chromosomes. Physical clastogens include X rays, ultraviolet light, cold shock, magnetic fields, and sound waves. Certain genes, viruses, and protozoa are examples of biological clastogens. This paper will deal primarily with chemical clastogens. Although the effects on human chromosomes are emphasized, it will sometimes be necessary to refer to experiments on animal and plant chromosomes. These are not irrelevant. In fact, there are no known plant clastogens to which animal chromosomes have been found to be immune. Many of the chemicals cited here have been tested on human cells only

Mutagenesis of cultured mammalian cells by x-radiation and ultraviolet light.

Abstract: The mutation of cultured Chinese hamster cells to 8-azaguanine resistance has been studied after ultraviolet and X-irradiation. Optimum numbers of induced mutants appeared after an expression time of 30–40 h before the addition of 8-azaguanine, and the yield of mutants tended to decrease when the initial number of cells in a 9 cm diameter plate exceeded 105. There was some evidence consistent with the hypothesis that cells resistant to 8-azaguanine are at a disadvantage at high cell densities in the absence of 8-azaguanine. An incubation period of at least 10 days after the addition of 8-azaguanine was necessary to detect the maximum number of induced mutants. Dose-response curves after exposure to ultraviolet light were linear in contrast to cumulative-type curves obtained after X-irradiation. A comparison of induced mutation rates for various species and cells after ionizing irradiation shows that the high mutability of animal cells compared with microorganisms does not appear to be correlated with the presence of meiotic stages but may be a general property of animal cells. The high mutability per unit dose of ionizing radiation, although not totally incompatible with a theory of DNA-located primary damage, could indicate that the “target” is large, for example a lysozome which when “hit” releases DNA-damaging enzymes through the nucleus. The results are discussed in terms of possible mechanisms and of the suitability of the system for routine mutagen screening.

Photopolymerizable dental products

Abstract: PHOTOPOLYMERIZALE DENTAL PRODUCTS ARE PROVIDED IN THE FORM OF COMPOSITIONS SUITABLE AS CMPOSITS RESTORATIVE MATERIALS, FISSURE SEALANTS, CEMENTS, ATIVITY LINERS AND RESTORAION GLAZES, THE COMPOSITIONS IN SITU, WITHIN THE ORAL ENVIRON PHOTOPOLYMERIZED IN SITU, WITHIN THE ORAL ENVIRONMENT, BY THE APPLICATION OF LIGHT ENERGY, SPECIFICALLY LIGHT ENERGY IN THE NEAL ULTRAVIOLET WAVE LENGTH BAND. SUCH A COMPOSITION IS MADE IN TWO PARTS, I.E. PASTE-PASTE, PASTE-LIQUID JELLY-POWDER, LIQUID-LIQUID ETC., WHEREIN ONE PHASE CONTAINS AN AROMATIC DIMETHACRYLATE MONOMER OR ADDUCT THEREOF WITH A MONO- OR DIISOCYANATE, A DILUENT MONOMER AND A POLYMERIZATION INHIBITOR, WHILE THE OTHER PHASE CONTANS A MATERIAL SENSITIVE TO ULTRAVIOLET LIGHT AND CAPABLE OF INITIATING FREE RADICAL POLYMERIZATION WHEN EXCITED THEREBY. OPTIONALLY, THE PASTE PHASES MAY CONTAIN FILLERS WHICH ARE CHARACTERIZED BY HAVING A REFRACTIVE INDEX NO GREATER THAN 0.075 DIFFERENT FROM THAT OF THE POLYMER RESULTING FROM THE FREE RADICAL POLYMERIZATION.

Effects of Caffeine on L-Cells Exposed to Mitomycin C

Abstract: Summary Mouse L-cells were grown in suspension culture and exposed to varying concentrations, from 0.2 to 4 μg/ml, of mitomycin C for periods ranging from 0.5 to 3.5 hr. A plot of cell colony-forming ability versus concentration of mitomycin C for different times of exposure yielded a series of exponential survival curves which were related by the fact that the product of the time of exposure and the concentration of mitomycin C required to reduce survival to 10% (C10) were a constant. However, the value of C10 was dependent on the pH of the cell culture at the time of exposure to mitomycin C. If, immediately after exposure to mitomycin C, the survival of the cells was measured in medium containing 2 mM caffeine, the C10 was 0.5 times that observed in the absence of caffeine. When the treated cells were incubated in the absence of caffeine for one generation time and their survival was measured in its presence, no difference in C10 over that observed in normal medium was seen. With a synchronous population of L-cells, evidence was obtained that cells exposed to mitomycin C which passed through their first DNA-synthetic period in the absence of caffeine had no additional loss of viability when plated in it at later times. These results indicate that the same system shown previously to exist in L-cells for the repair or alteration of ultraviolet light damage is also functional against damage produced by mitomycin C.

Gamma-ray-resistant and -sensitive strains of slime mold (Dictyostelium discoideum).

Abstract: The vegetative cells and spores of the cellular slime mold Dictyostelium discoideum NC-4 are very resistant to60 Co gamma rays, with a 10% survival dose ( D10) of 300 krad in air. Using ultraviolet light or nitrosoguanidine as a mutagenic agent and replica plating with gamma irradiation as a selective agent, we have isolated several stable daughter strains that are more sensitive to gamma rays. A comparison of some of the radiation responses of the parent (NC-4; wild type), γs-18 ( ${\rm D}_{10}=75\ {\rm krad}$), and γs-13 ( ${\rm D}_{10}=4\ {\rm krad}$) strains has been made. All three strains show the same gamma-ray-induced division delay of about 1 cell generation time for 54 krad. Strains wt (wild type) and γs-18 show split-dose recovery of colony-forming ability but γs-13 does not. For wt, this recovery is temperature-dependent with a maximum at 23°C, the most favorable growth temperature. Some recovery still occurs at 5-10°C, although growth does not. Strains wt and γs-18 are more sensitive when irr...

Optical reader for luminescent codes luminescing in different wavelengths

Abstract: Symbols formed by marking a substrate with coded inks, the coding represented by the absence or presence in one or more levels of one or more photoluminescent components, are irradiated with ultraviolet light and the photoluminescence from the various coding components is projected through a dispersing agent, such as a prism or a grating, onto the sensitive surface of a television camera tube, such as a vidicon or orthicon, the output of the camera tube producing electrical pulses in each scan corresponding to the position of the various photoluminescent colors. The output can be read out on an oscilloscope or other readout device synchronized with the television camera electron scan. The presence of coding components are represented by pulses in corresponding positions and the height of the pulses can represent the level of component concentration if it is present in more than one concentration.

Different modes of loss of photoreversibility of ultraviolet light-induced true and suppressor mutations to tryptophan independence in an auxotrophic strain of Escherichia coli

Abstract: The loss of photoreversibility of UV-induced mutations to tryptophan independence in a tryptophan-requiring strain of E. coli (left after “ mutation frequency decline ”, produced by incubation in the absence of the amino acid, has eliminated most suppressor mutations) occurs during the first 20 min of postirradiation incubation. It is amino acid independent but is blocked by dinitrophenol. It is independent of DNA replication since it occurs in the presence of nalidixic acid, an inhibitor of DNA replication. Loss of photoreversibility of the suppressor mutations (subject to mutation frequency decline ) occurs in correlation with the initial doubling of DNA in the culture and may be prevented by nalidixic acid, suggesting that DNA replication is required for such loss. The initial postirradiation replication of DNA is significant to the mutation process since expression of both sorts of mutation (measured on tryptophan-free minimal agar medium) does not occur unless DNA synthesis is allowed before plating and is prevented by nalidixic acid. The data are consistent with the hypothesis that dimer excision accounts for loss of photoreversibility of stable reversions to tryptophan independence but that DNA replication is necessary to this process for suppressor mutations of this requirement subject to mutation frequency decline .

Common Steps in the Repair of Alkylation and Radiation Damage in Yeast

Abstract: Radiation sensitive mutants of Saccharomyces cerevisiae were exposed to the action of nitrogen mustard (HN2) and methyl methanesulfonate (MMS). Sensitivity to HN2 was found to be correlated with sensitivity to ultraviolet light, whereas sensitivity to MMS was found to be correlated with sensitivity to X-rays. One mutant strain that is sensitive to both UV and X-rays was found to be sensitive also to HN2 and MMS. The latter result shows that there exists a locus in yeast that controls the repair of DNA damaged by all four of these mutagens.

Effect of Formalin, β-Propiolactone, Merthiolate, and Ultraviolet Light Upon Influenza Virus Infectivity, Chicken Cell Agglutination, Hemagglutination, and Antigenicity

Abstract: Four strains of influenza virus were treated with Formalin, Merthiolate, Merthiolate and Formalin, ultraviolet light, and beta-propiolactone (BPL) for 18, 48, and 72 hr. Infectivity, chicken cell agglutination (CCA), hemagglutination (HA), and antigenicity determinations were made. Except for Merthiolate, each method of inactivation was equally effective in reducing infectivity. Loss of infectivity was related to length of treatment. CCA determinations were higher for all treated groups except for BPL-treated samples; these had lower determinations. BPL treatment also lowered the HA titer. Antigenicity was lessened by BPL treatment and by Merthiolate and Formalin treatment. Generally, the length of inactivation up to 72 hr did not affect CCA, HA, or antigenicity determinations. For the most part, there was no significant differences in the reactivity of the four strains.

Sunlight-induced Pyrimidine Dimers in Human Cells in Vitro

Abstract: PYRIMIDINE dimers have been implicated in much ultraviolet light induced damage in bacteria1, and it has been shown that they can be induced in mammalian cells with short wavelength ultraviolet light2–7. In placental mammals, pyrimidine dimers are not repaired by direct monomerization by photoreactivating light2,8,9, although a dark repair mechanism, somewhat similar to that found in bacterial cells, has been demonstrated10.