Showing papers on "Ultraviolet light published in 1971"

Mutants of yeast defective in mutation induced by ultraviolet light.

Abstract: NDUCED mutations are thought to arise as a result of enzymatic processes uti‘lizing DNA damage as a substrate (BRIDGES 1969). Although the molecular mechanism is not known, evidence reviewed by WITKIN (1969) suggests that in E. coli mutations are produced during postreplication repair of lethal damage induced by ultraviolet light (UV) and controlled by r e d and ezrf (or lexf) genes. Strains carrying rec or ezr, although normal in excision repair, exhibit reduced or no UV mutability compared to wild type. In addition, such strains are UV sensitive, X-ray sensitive, and recombination deficient in varying degrees ( WITKIN 1969). In previous studies of UV-induced mutation in fungi, UV-sensitive strains have been selected on the assumption that UV mutagenesis might be related to dark repair of lethal damage. In some of these UV-sensitive strains, the frequencies of UV mutation are reduced compared to wild type at equal UV doses (CHANG, LENNOX and TUVESON 1968; NASIM 1968; WOHLRAB and TUVESON 1969). whereas in others these frequencies are enhanced (AVERBECK et al. 1970; RESNICK 1969; ZAKHAROV, KOZINA and FEDOROVA, 1970). To identify new genes controlling UV-induced mutation, it is desirable to select strains directly for defective mutation induction, thereby avoiding the prior condition that all such mutants be UV-sensitive. Mutants of Saccharomyces cereuisiae were selected ( LEMONTT and MORTIMER 1970) for reduced ability to undergo UV-induced locus reversion of the ochresuppressible (GILMORE 1967; HAWTHORNE 1969) argl-17 allele. This paper describes the isolation and some characteristics of these “reversionless” mutants, The results are discussed in relation to current ideas about induced mutagenesis.

Highly reflective thermoplastic bodies for infrared, visible or ultraviolet light

Abstract: Highly reflective colored plastic film is prepared from transparent plastics having no pigment or inorganic material by forming the film from a number of layers of different thermoplastic materials which differ in refractive index and the layer thicknesses are from about 0.05 micron to about one micron.

The radiation response of human malignant melanoma cells grown in vitro.

Abstract: Summary The three malignant melanoma cell lines used are characterized by having high, intermediate , and low quantities of pigment production. The response of these malignant melanoma cells to X-ray in vitro does not correlate with a model of the classically radioresistant tumor cell that clinical experience might predict. The in vitro melanoma cells were only slightly more resistant to X-rays than the nontumor in vitro Chinese hamster ovary cell line tested. The responses to X-rays of all three melanoma lines were the same ( n = 40, D 0 = 100 rads). The response to ultraviolet light varied with the amount of pigment present in each cell line. The strain producing a high quantity of pigment was the most UV resistant ( n = 3, D 0 = 57 ergs/sq mm). The strain producing a low pigment quantity was the most UV sensitive ( n = 3, D 0 = 31 ergs/sq mm). All melanoma strains were more resistant to UV than the Chinese hamster ovary cell line ( n = 10, D 0 = 20 ergs/sq mm). Survival determinations made as a function of time between two fractionated UV doses of 100 + 100 ergs/sq mm indicated that these melanoma cells possessed ability to recover from sublethal UV damage.

Bacteriophage and the Toxigenicity of Clostridium botulinum Type C

Abstract: Nontoxigenic and bacteriophage-sensitive bacterial cultures have been isolated from toxigenic Clostridium botulinum type C, strain 468C, after treatment with either ultraviolet light or acridine orange. Two bacteriophages, designated CEbeta and CE(gamma), were isolated from toxigenic strain 468C. Both of these bacteriophages were capable of infecting the nontoxigenic type C cultures, but only bacteriophage CEbeta was involved in the change from nontoxigenicity to toxigenicity.

Caries Prevention in Pits and Fissures Sealed with an Adhesive Resin Polymerized by Ultraviolet Light: A Two-Year Study of a Single Adhesive Application

Abstract: Examinations were made to determine the protection from caries 1½ and two years after the sealing of 200 pits and fissures of deciduous and permanent teeth surfaces with an adhesive resin polymerized by ultraviolet light. After two years, a single application of the adhesive to the surfaces of permanent teeth had resulted in a 99% caries reduction; there was an 87% reduction of caries in the pits and fissures of the occlusal surfaces of the deciduous teeth. Adhesive sealing could be useful in preventive dentistry because it is intended for the caries-susceptible areas that are least benefited by fluoride.

Amorphous silicon film as a uv filter

Abstract: There is disclosed the use of a thin amorphous silicon film as a narrow-band rejection filter which is used either as a mask to UV light in semiconductor device processing or is used as a protective shield for solar cells which overheat in the presence of ultraviolet light.

The excision of pyrimidine dimers from DNA of ultraviolet irradiated yeast.

Abstract: It is shown that pyrimidine dimers formed by ultraviolet light in the DNA of haploid Saccharomyces cerevisae are removed under the influence of photoreactivating light and also in the dark under growth conditions. The integrity of the rad 1 locus is necessary for the dark-removal of dimers.

Ultraviolet Light-induced Formation of Pisatin and Phenylalanine Ammonia Lyase.

Abstract: The production of pisatin is induced3 in pea tissue by various plant pathogens (4, 8). This de novo synthesis can also be induced by an array of chemicals (9, 19, 22), most of which are known to have an affinity for double stranded DNA. Also, most of the inducers of pisatin or phenylalanine ammonia lyase (PAL)', EC 4.3.1.5 (a key enzyme in the biosynthesis of pisatin) have the potential to change the conformation of DNA. The induction of both pisatin and PAL is dependent on new RNA and protein synthesis (9, 22). We have proposed (9, 22) that the control of these cellular responses occurs at the gene transcription level and depends on the conformational state of the double stranded DNA (i.e., the DNA becomes more transcribable either by dissociating a repressor component or by assuming a more desirable conformation for transcription). If conformational changes in cellular DNA do, in fact, initiate this response, ultraviolet light which can dimerize thymidine bases and cause lesions in DNA (5, 23) should also influence this response. This paper describes the induced synthesis of pisatin and PAL by ultraviolet light.

Photocatalytic production of organic compounds from CO and H2O in a simulated Martian atmosphere

Abstract: [14C]CO2 and [14C]organic compounds are formed when a mixture of [14C]CO and water vapor diluted in [12C]CO2 or N2 is irradiated with ultraviolet light in the presence of soil or pulverized vycor substratum. The [14C]CO2 is recoverable from the gas phase, the [14C]organic products from the substratum. Three organic products have been tentatively identified as formaldehyde, acetaldehyde, and glycolic acid. The relative yields of [14C]CO2 and [14C]organics are wavelength- and surface-dependent. Conversion of CO to CO2 occurs primarily at wavelengths shorter than 2000 A, apparently involves the photolysis of water, and is inhibited by increasing amounts of vycor substratum. Organic formation occurs over a broad spectral ranger below 3000 A and increases with increasing amounts of substratum. It is suggested that organic synthesis results from adsorption of CO and H2O on surfaces, with excitation of one or both molecules occurring at wavelengths longer than those absorbed by the free gases. This process may occur on Mars and may have been important on the primitive earth.

DNA repair in ultraviolet light irradiated HeLa cells and its reversible inhibition by hydroxyurea.

Abstract: — –The repair of u.v. damaged DNA in HeLa cells can be detected using the alkaline sucrose gradient technique. As a result of pyrimidine dimer excision single strand breaks are produced in DNA of irradiated cells. Rejoining of these breaks occurs during an 8 hr post-irradiation incubation period and is prevented by hydroxyurea and acriflavine. The inhibition of repair by hydroxyurea can be reversed by a mixture of all 4 deoxyribonucleosides at a concentration that does not reverse the inhibition of total DNA synthesis.

Phytochrome-mediated flavone glycoside synthesis in cell suspension cultures of Petroselinum hortense after preirradiation with ultraviolet light

Abstract: Ultraviolet light was demonstrated to stimulate flavone glycoside synthesis in Petroselinum cell suspension cultures. The data presented suggest the involvement of phytochrome in this response: Flavone glycoside formation resulting from 1 h of ultraviolet irradiation was increased by subsequent continuous far-red light irradiation. However, the ultraviolet effect was reduced by a subsequent irradiation with 10 min of far-red. This far-red effect was fully reversed by a sub-sequent irradiation with 10 min of red. Red and far-red irradiations were ineffective without ultraviolet preirradiation. It is concluded that in this system ultraviolet irradiation is required in order to change the cells in such a way as to allow a physiological effectiveness of the phytochrome system.

Formation of a Carcinogen in Human Skin irradiated with Ultraviolet Light

Abstract: THE role of ultraviolet light and sunlight in the aetiology of certain types of human skin cancer is now well established1. The mechanism(s) by which light induces such changes, however, are not understood. One explanation2,3 of the induction of skin cancers by ultraviolet light and sunlight is that steroids in the skin are converted photochemically to carcinogenic materials, but failure to obtain such compounds by irradiation of naturally occurring sterols in biological systems has cast doubt upon the validity of such a hypothesis. Although Blum has argued against this hypothesis4, he has recently described the induction by ultraviolet radiation of a diffusible substance that mediates hyperplasia5. Here we provide evidence for the formation of a cholesterol-derived carcinogenic photoproduct in human skin.

Histopathology of in vitro caries developing around silver amalgam fillings.

Abstract: On clinically sound buccal and lingual surfaces of 130 extracted teeth, class V cavities were prepared and filled. In some cases previously filled teeth were used. In vitro caries around the fillings was produced by immersing the teeth in an acid-gelatin system, the pH of which was held within the values 4.0–5.2 by means of lactic acid. Duration of the experiments varied within the range of 5–200 days. A number of teeth which were filled, but not exposed to the acid gelatin, were used as controls. Ground sections in series were prepared through the teeth with the fillings in situ and studied by ordinary transmitted and incident light, polarized light, ultraviolet light, and microradiography. The lesions produced consisted of two regions, the outer lesion and the cavity wall lesion. In the enamel the shape of the former and its relation to the latter seemed to be influenced by the angle made by the cavity wall with the prisms. The outer lesion developed by an action on the outer surface of the enamel or cementum and showed the features of a primary attack. Usually the wall lesion was a narrow subsurface defect in the enamel or the enamel and the dentine of the cavity wall. It represented an initial stage of the caries process and gradually encompassed the whole filling without penetrating deeply into the tissue. The development of the wall lesion was determined by the amalgam-dental tissue interface into which hydrogen ions must have diffused from the acidified gelatin. The demineralization seemed to have acted perpendicularly to the surface of the cavity wall in which reprecipitation had taken place in a few cases.

Identification of Proteins Coded in Phage Lambda

Abstract: Phage λ has sufficient DNA to encode about 50 proteins of molecular weight 33,000, and about 35 genes are known. However, fewer than ten λ proteins have been studied in any detail, largely because of the lack of specific assays for the others, and because host protein synthesis continues after infection by λ . This paper describes the labeling, identification, and characterization of λ proteins by a technique devised by Ptashne which circumvents these problems. The proteins identified belong to both the early and late classes, and several are products of genes which have not been described previously. EXPERIMENTAL METHOD The basic method used here to characterize λ proteins is to label them with radioactive amino acids and to compare the electrophoretic patterns of radioactive proteins obtained from various mutants. These experiments depend on the fact, first reported by Ptashne, that infection by wild-type λ ( λ + ), of cells heavily irradiated with ultraviolet light (UV), stimulates the ability of the cells to incorporate radioactive leucine into TCA-insoluble material by 10–15-fold (Ptashne, 1967). This technique makes it possible to label phage-specific proteins without an intolerable level of labeling of Escherichia coli proteins. Synthesis of Early and Late λ Proteins in Irradiated Bacteria Figure 1 shows the dependence of total leucine incorporation on UV dose for uninfected cells and for cells infected with three different phages. The ratio of incorporation between λ + -infected and uninfected cells can be seen to increase with dose up to about 12,000 erg/mm 2 and then to remain approximately constant.

DNA synthesis in differentiating skeletal muscle cells: initiation by ultraviolet light.

Abstract: As skeletal muscle cells differentiate, they fail to initiate DNA synthesis. This rigid regulation, which persists even after cells are fully developed, does not extend to "repair" DNA synthesis, in that ultraviolet light initiates DNA synthesis in 99 percent of the muscle nuclei exposed. The rate of "repair" DNA synthesis in these nuclei, however, drops over 50 percent at the time of cell differentiation.

Relative susceptibility of acid-fast and non-acid-fast bacteria to ultraviolet light.

Abstract: Mycobacterium tuberculosis strain Erdman, M. bovis (BCG), and M. phlei showed a 1- to 2-log drop in viability after exposure to ultraviolet light compared to a 5-log drop over the same period for Staphylococcus albus, Listeria monocytogenes, Escherichia coli, Pseudomonas aeruginosa, Salmonella enteritidis, and Serratia marcescens. L. monocytogenes showed an initial resistance to ultraviolet inactivation, but later the inactivation rate increased sharply. The significance of these findings with regard to the use of S. marcescens as a test organism for determining the bactericidal efficiency of ultraviolet lamps used to sterilize equipment contaminated with tubercle bacilli is discussed.

Photolysis Mapping Studies of Aliphatic Carbonyl Compounds

Abstract: The photolysis mapping technique is a marriage of an old radical detecting system with the following principle: If polarized light is used for photodissociation, the flux of fragments will be anisotropic because the molecular absorption is anisotropic in the molecular axis system. The simplest aliphatic carbonyl compounds (formaldehyde, acetaldehyde, propionaldehyde, and acetone) were photodissociated using polarized ultraviolet light. The gases were held at such a low pressure that the fragments travel to the walls without collision in the gas phase. On the walls the radicals were detected by the old mirror removal technique. There is a substantial anisotropy of removal. The sense of the anistropy is different for the different molecules, being perpendicular for formaldehyde and acetone, and parallel for acetaldehyde and propionaldehyde. These results are interpreted by assuming that the carbonyl compounds all become nonplanar in the excited state and the ultimate direction of the fragments can be inferr...

Insect visual pigment sensitive to ultraviolet light.

Abstract: BEHAVIOURAL1,2 and electrophysiological3 experiments have shown that the insect eye responds to ultraviolet irradiation. In the eye of the honeybee there is only a small population of special ultraviolet receptors, which are involved in colour vision. In the compound eye (superposition type) of Ascalaphus macaronius Scop. (Neuroptera, Ascalaphidae) there are two different morphological spheres. The so called frontal eye is sensitive only to ultraviolet radiation, whereas the lateral eye also responds to green light4. For this reason, the frontal eye seemed to us a suitable source from which to try to extract the ultraviolet-sensitive photopigment of an insect.

Altered Deoxyribonucleic Acid Polymerase Activity in a Methyl Methanesulfonate-Sensitive Mutant of Bacillus subtilis

Abstract: Of six deoxyribonucleic acid repair mutants of Bacillus subtilis assayed for deoxyribonucleic acid polymerase, only the methyl methanesulfonate-sensitive and ultraviolet light-sensitive mutant JB1-49(59) has impaired polymerase activity. Extracts prepared by sonic treatment or gentle lysis had about 10% of the wild-type activity with poly d(A-T), an alternating copolymer of deoxyadenylate and deoxythymidylate, used as template. The sensitivity to methyl methanesulfonate and ultraviolet light and the low level of polymerase activity transformed and reverted together, indicating that the two characteristics are a pleiotropic manifestation of a single mutation. Mixed extract and kinetic experiments mitigated against an altered nuclease activity as the enzymatic consequence of the mutation. Also, the mutant and wild type activities were stimulated equally by Escherichia coli exonuclease III. The residual activity in the mutant showed several differences from the wild-type activity: it purified differently, was more sensitive to sulfhydryl reagents, and displayed a different template specificity. We tentatively conclude that either the mutation in JB1-49(59) has introduced a qualitative as well as a quantitative change in the polymerase or the wild type contains two distinct polymerases, one of which is missing in the mutant.

Familial progressive hyperpigmentation.

Abstract: Familial progressive hyperpigmentation is a distinctive, dominantly inherited genodermatosis, characterized by patches of hyperpigmentation present at birth which increase in size and number with age. In contrast to normal areas, the epidermis of the dark skin and mucous membranes appears to show an increase in number and average size of melanin granules, and seemingly more premelanosomes. Genetic findings from one family coupled with glucose-6-phosphate dehydrogenase studies were not conclusive enough for determining whether the inheritance pattern was autosomal or sex-linked. Additional genetic studies, sex chromatin counts, chromosome analysis, determinations of circulating tyrosinase and pituitary-adrenal hormone levels, porphyrin determinations, urinary and plasma aminograms, and other laboratory and clinical investigations failed to elucidate the pathogenesis. Normal and hyperpigmented skin showed no differences in 3,4 dihydroxyphenylalanine-positive cell counts, histopathology of the dermis, temperature, response to ultraviolet light, or thermal and methacholine-chloride-induced eccrine sweating.