THE INFLUENCE OF SEMI-DEHYDRATION ON THE RESPONSE OF STREPTOCOCCUS LIQUEFACIENS TO ULTRAVIOLET LIGHT

Abstract— The effect of relative humidity on the survival and sensitivity to radiations of Streptococcus liquefaciens has been studied. The micro-organism was found to be little affected by dehydration in aerosols and its sensitivity to the lethal action of 2537 Å light to be unaffected by changes in the relative humidity at which the cells were held during irradiation. The cells were more stable to the lethal action of 3200–4000 Å, however, when they were held at 70% relative humidity than at 50 or 30% relative humidity. Mutant cells unable to liquify gelatine were induced by semi-dehydration at 50% relative humidity and their numbers were increased by concomitant irradiation with 3200–4000 Å light. This type of mutant was not observed when the cells were irradiated with 2537 Å light. Mutant cells which had a different response from that of the parent cell to the presence of oxygen in their growth medium were produced by both wavebands of light, but only when the cells were held at 50% relative humidity. It is proposed that semi-dehydration stresses the cell membrane and damages those parts of the bacterial DNA associated with the membrane. Concomitant irradiation is suggested to enhance this particular effect.     

SENSITIVITY OF MARINE PHYTOPLANKTON TO UV-B RADIATION: IMPACT UPON A MODEL ECOSYSTEM

Abstract Human activities may cause a 16% reduction of stratospheric ozone. The concomitant increase in solar UV-B radiation reaching the surface of the earth could detrimentally affect the phytoplankton that form the base of the food web in oceanic and estuarine ecosystems. In the current study acute exposure of seven species of marine phytoplankton to UV–B radiation depressed the radiocarbon estimate of primary production. A model of a marine ecosystem was constructed based on the differential sensitivities of the seven species of phytoplankton. Increasing the UV–B exposure within the model from 100 Eff_DNAJ/m²/day to 150 Eff_DNAJ/m²/day significantly altered the community composition of the ecosystem. In nature, alteration of the phytoplanktonic community structure could result in a significant impact upon successional patterns and primary producer–consumer trophodynamics.     

THE EFFECT OF CHANGES IN CELL GEOMETRY ON THE SENSITIVITY TO ULTRAVIOLET RADIATION OF MAMMALIAN CELLULAR CAPACITY

Abstract— We have measured a calcium and magnesium dependent change in cell shape when mammalian cell monolayers are being prepared for irradiation by replacing their growth medium with certain buffers. In some cases, flattened cells (umbonate) assumed a spherical configuration. In order to assume a centrally located target molecule, we used a DNA-dependent cellular function–pacity for herpes viral growth–as the parameter to measure ultraviolet (UV) sensitivity of cells irradiated while in either of the two shapes. Umbonate cells were more sensitive to UV than were spherical cells. Exposures to the cell that lowered the cellular capacity of umbonate cells to the 10% survival level only lowered spherical cells to the 50% level. Twenty-seven per cent additional UV exposure to spherical cells was required to get the same effect as with umbonate cells. Included in the text are photographs of both cell types, survival curves for cellular capacity, a measure of the absorbance of cell homogenates, and a calculation of the relative number of photons absorbed by each cell nucleus.     

FORMATION OF PROTEIN-BOUND 3,4-DIHYDROXYPHENYLALANINE IN COLLAGEN TYPES I AND IV EXPOSED TO ULTRAVIOLET LIGHT

Abstract— Collagen was exposed to an ultraviolet (UV) lamp that emitted predominantly in the UVB range. The cross-linking of collagen type I and type IV by UV irradiation was observed. Amino acid analyses revealed that Tyr residues in both collagen types I and IV were decreased by irradiation. In collagen type IV, losses of His and Met residues were also observed. These losses of collagen type IV may be due to the degradation of Trp, which exists in collagen type IV and decreased drastically during UV irradiation. To clarify the mechanism of Tyr modification in both types of collagen, the degradation products of Tyr were analyzed. Dityrosine, which is a dimer of the Tyr residue, could not be detected in the acid hydrolysates of UV-irradiated collagen. However, 3,4-dihydroxyphenylalanine, DOPA, was detected in the hydrolysates using HPLC with an electrochemical detector. The amounts of DOPA in the acid hydrolysates of collagen exposed to UV light for 24 h were approximately 350 pmol/mg protein (collagen type IV) and 80 pmol/mg protein (collagen type I). The DOPA formed may partially contribute to photoaging of the skin.     

THE INFLUENCE OF NUTRITION ON THE DNA CONTENT OF ESCHERICHZA COLI AND ITS RESPONSE TO ULTRAVIOLET LIGHT

Abstract— The influence of nutrition on the sensitivity of Escherichia coli 15 T- to ultraviolet light (u.v.) and the synthesis of DNA has been studied. Growth in media containing glucose or NH,⁺ has been found to endow cells with a greater resistance to lethal u.v. damage than those grown in media containing succinate or amino acids, respectively. In addition, the sensitivity of the lactose ( lac ) locus of the DNA to mutagenic damage has been found to be altered by changes in the carbon supply but not by changes in the nitrogen source, while the sensitivity of loci controlling amino acid synthesis was altered by changes in the nitrogen source but not in the carbon source. Cells fed with glucose or NH₄⁺ have been found to possess more DNA than cells fed with succinate or amino acids, respectively. The data indicate that the type of carbon and nitrogen supplied to the cells will determine whether or not set regions of the DNA will undergo more than one round of replication. The presence in the cell of identical genetic loci either in duplicate or in multiples, directed by the particular types of carbon and nitrogen supplied, is suggested to be, in part, the reason why an alteration in nutrition is able to influence the sensitivity of bacterial cells to radiation.     

ULTRAVIOLET IRRADIATION OF NUCLEIC ACIDS COMPLEXED WITH HEAVY ATOMS—III. INFLUENCE OF Ag + AND Hg 2+ ON THE SENSITIVITY OF PHAGE AND OF TRANSFORMING DNA TO ULTRAVIOLET RADIATION

Abstract— We have studied the influence of the heavy metal ions Ag⁺ and Hg²⁺ on the photoinactivation and photodimerization of transforming DNA and of bacteriophage. The rate of inactivation of Haemophilus influenzae transforming DNA by ultraviolet (UV) radiation was enhanced by a factor of 30 when it was complexed with Ag⁺. This enhancement was correlated with a comparable increase in the rate of thymine dimerization. In contrast, mercuric ions led to a reduction in the rates of both inactivation and dimerization. When we examined the effects of these metal ions on the photobiology of bacteriophage, we again found that Ag⁺ enhanced and Hg²⁺ reduced the rate of ultraviolet inactivation. These results demonstrate that heavy metals may be useful tools for studying the photochemistry and photobiology of nucleic acids.     

DELAYED PLATING RECOVERY OF DIPLOID YEAST EXPOSED TO ULTRAVIOLET LIGHT BETWEEN 254 AND 313 nm WAVELENGTH

Abstract— Diploid yeast cells exposed to UV-light of different wavelengths in the region between 254 and 313 nm were assessed for their ability of delayed plating recovery. They were either held in non-nutrient suspension ('liquid holding') or on non-nutrient agar before final plating. Thus it was possible to distinguish between real and apparent recovery due to cell multiplication. The experiments showed that no delayed plating recovery was found beyond 295 nm wavelength UV.     

REVERSION PROFILES OF COOL WHITE FLUORESCENT LIGHT COMPARED WITH FAR ULTRAVIOLET LIGHT: HOMOLOGIES AND DIFFERENCES

Abstract— General Electric and Sylvania 15 W coolwhite fluorescent lamps emit roughly 6% of their total irradiance as light in the UV spectrum. Illumination of sensitive Salmonella tester strains results in both lethal and mutagenic activities. In contrast, comparable Philips lamps emit lower levels of U V light, especially UVB, and exhibit no detectable lethal or mutagenic effects. The spectra of mutations induced by General Electric coolwhite lamps in histidine-requiring base substitution mutants hisG46 and hisG428 ("reversion profiles") resemble mutagenesis by far UV light (UVC) and differ quite markedly from the spectra of mutations that occur spontaneously. Coolwhite and UVC reversion profiles are not identical, however. The percentage of C to A transversion mutations induced in hisG46 are elevated over those found after UVC treatment, and a strong bias for one particular class of tandem base substitutions (TAA → T GT ) prevails after treatment of hisG428 with coolwhite light, a bias not observed with UVC. Increased attention needs to be given to minimization of exposure to UV light from fluorescent lamps commonly used in homes and workplaces.     

SITES SENSITIVE TO S1 NUCLEASE and DISCONTINUITIES IN DNA NASCENT STRANDS OF ULTRAVIOLET IRRADIATED MOUSE CELLS

Abstract Mouse 3T3 cells irradiated with ultraviolet light synthesize DNA containing sites sensitive to the single-strand specific SI nuclease. The appearance of these sites correlates well with the presence of discontinuities in nascent strands, detected by the methodology of sedimentation in alkaline sucrose gradient. Thus, both the sites sensitive to SI nuclease and the discontinuities in nascent strands (i) are stabilized by caffeine; (ii) are no longer formed late after irradiation and (iii) disappear faster when a certain UV fluence is split into two fluences whose sum equals the single fluence. Moreover, the recovery in synthesizing DNA without SI sensitive sites is not dependent on excision repair of pyrimidine dimers or on continuous DNA synthesis. These SI sensitive sites are exclusive of replicative structures of irradiated cells and should correspond to stretches of single-strand DNA (gaps) formed during replication.     

ACTINIC RETICULOID–AN IDIOPATHIC PHOTODERMATOSIS WITH CELLULAR SENSITIVITY TO NEAR ULTRAVIOLET RADIATION

Abstract— Long wavelength UV radiations (320–400 nm) cause persistent inhibition of RNA synthesis and marked cytopathic changes in fibroblasts from patients with actinic reticuloid (AR) but not in those from patients with Bloom syndrome or xeroderma pigmentosum. Furthermore, the AR cells show abnormal DNA fragmentation when they are irradiated at temperatures compatible with enzyme activity. Germicidal UVR ( ca . 95% 254 nm) stimulates DNA repair synthesis and inhibits DNA replication to a normal extent in the AR cells.
Thus, actinic reticuloid, a severe photodermatosis, characterised by skin sensitivity to UV-B, UV-A and part of the visible spectrum and by infiltrates reminiscent of mycosis fungoides, is a human disease with in vitro cellular sensitivity to UV-A and, to our knowledge, is also the first to be reported.
We advance the hypothesis that inefficient cellular neutralisation of free radicals may explain the cellular phenotype of actinic reticuloid and contribute to the establishment of a vicious circle that would favour the chronic clinical course and persistent lympho-histiocytic skin infiltrates characteristic of the disease.     

ULTRAVIOLET LIGHT IRRADIATION OF DEFINED-SEQUENCE DNA UNDER CONDITIONS OF CHEMICAL PHOTOSENSITIZATION

Abstract— The formation of cyclobutane pyrimidine dimers and UV light-induced (6-4) products was examined under conditions of triplet state photosensitization. DNA fragments of defined sequence were irradiated with 313 nm light in the presence of either acetone qr silver ion. UV irradiation in the presence of both silver ion and acetone enhanced the formation of TT cyclobutane dimers, yet no (6-4) photoproducts were formed at appreciable levels. When photoproduct formation was also measured in pyrimidine dinucleotides, only cyclobutane dimers were formed when the dinucleotides were exposed to 313 nm light in the presence of photosensitizer. The relative distribution of each type of cyclobutane dimer formed was compared for DNA fragments that were irradiated with 254, 313, or 313 nm UV light in the presence of acetone. The dimer distribution for DNA irradiated with 254 and 313 nm UV light were very similar, whereas the distribution for DNA irradiated with 313 nm light in the presence of acetone favored TT dimers. Alkaline labile lesions at guanine sites were also seen when DNA was irradiated with 313 nm light in the presence of acetone.     

CHANGES IN TRANSMISSION CHARACTERISTICS OF POLYMETHYLMETHACRYLATE AND CELLULOSE (III) ACETATE DURING EXPOSURE TO ULTRAVIOLET LIGHT

Abstract— Ultraviolet-transparent polymethylmethacrylate (PMMA) and cellulose (III) acetate (CA) (often used as a cut-off filter in UVB [280–320 nm] biological effect studies) were exposed to a 20 W Philips TL 12 lamp to examine changes in transmission characteristics due to UVB exposure. Transmission of UVB and biologically weighted UVB (UV_BE(DNA)) through PMMA were similar, 88.3 and 83.5%, respectively. The absorption characteristics of PMMA did not change with time at any of the UV irradiance levels applied. However, transmission of UVB and UVB_BE(DNA)) through new CA differed considerably: 59% versus only 11%, respectively. Also, spectral absorption characteristics changed with time due to degradation of CA, at a rate that was dependent on the incident UVB irradiance. The decrease in transmission through CA of both UVB and UV_BE(DNA) can be described by exponential functions. The CA that was wrapped around the UV lamp showed dramatic changes in UV absorption over the first few hours of use. However, when CA was placed at a longer distance from the light source initial degradation was less. It is concluded that PMMA can be applied in UV effect studies as a reasonable alternative for quartz. The CA should, however, be used with care, because the large transmission decreases that were observed strongly hamper an accurate calculation of (biologically weighted) UVB dose rates.