A comparison of five effects of ultraviolet light on the Arbacia egg

The demonstration of five different effects of ultraviolet radiation on the sea urchin's egg indicates that more than one basic photochemical process goes on there. Photorecovery is observed in only one of these. The need for caution in interpreting such effects is obvious. Evidence for a different mechanism for the timing of cleavage in eggs activated by ultraviolet radiation as compared to normally fertilized eggs is presented. The bearing of these studies on survival curves for microorganisms is discussed.     

Delay of cleavage of the Arbacia egg by ultraviolet radiation

While our data do not permit us to state the exact locus or mode of action of ultraviolet radiation in the Arbacia egg, certain general conclusions may be reached. The amount of delay of cleavage of these eggs is determined by two principal factors: (1) The extent of an effect, resulting from photochemical action induced by ultraviolet radiation, which is reversible in a biological sense, the reversibility not being directly dependent upon the process of cell division. (2) The sensitivity of the cell division process to the effects of the ultraviolet-induced photochemical reaction. This factor varies with the stage of cell division, the cell being insensitive during a period corresponding to most of mitosis. It seems likely that these findings may apply to cell division in general, but, since the quantitative relationships observed must, in this case, reflect the integration of two semi-independent factors, the over-all picture may appear quite different for different kinds of cells.     

The accelerating action of illumination in recovery of Arbacia eggs from exposure to ultraviolet radiation

Light of wave lengths 0.30µ to 0.50µ, accelerates return of the cleavage rate of Arbacia eggs to normal, after delay by exposure to ultraviolet radiation (wave lengths 0.238µ to 0.31µ). Recovery is apparently complete. Wave lengths 0.30µ to 0.50µ have no effect on the cleavage rate of normal eggs, nor does such illumination previous to dosage with ultraviolet radiation influence subsequent recovery. Acceleration of recovery of the egg occurs before fertilization as well as after. The effects of ultraviolet radiation and recovery therefrom are essentially the same in nucleated "white halves" as in the intact eggs. This phenomenon in the Arbacia egg seems basically comparable to photoreactivation of bacteria and fungi.     

Characterization in vitro and in vivo of the DNA helicase encoded by Deinococcus radiodurans locus DR1572

Deinococcus radiodurans survives extremely high doses of ionizing and ultraviolet radiation and treatment with various DNA-damaging chemicals. As an effort to identify and characterize proteins that function in DNA repair in this organism, we have studied the protein encoded by locus DR1572. This gene is predicted to encode a Superfamily I DNA helicase, except that genome sequencing indicated that it has a one-base frameshift and would not encode a complete helicase. We have cloned the gene from two different D. radiodurans strains and find that the frameshift mutation is not present. The corrected gene encodes a 755 residue protein that is similar to the Bacillus subtilis YvgS protein and to helicase IV of Escherichia coli. The purified protein (helicase IV_Dr) has ATP hydrolysis and DNA helicase activity. A truncated protein that lacks 214 residues from the N-terminus, which precede the conserved helicase domain, has greater ATPase activity than the full-length protein but has no detectable helicase activity. Disruption of locus DR1572 in the D. radiodurans chromosome causes greater sensitivity to hydrogen peroxide and methyl-methanesulfonate compared to wild-type cells, but no change in resistance to gamma and ultraviolet radiation and to mitomycin C. The results indicate that locus DR1572 encodes a complete protein that contributes to DNA metabolism in D. radiodurans.     

Selection of Autographa californica nuclear polyhedrosis virus for resistance to inactivation by near ultraviolet,far ultraviolet,and thermal radiation

Experiments were performed to isolate strains of Autographa californica nuclear polyhedrosis virus (Baculovirus) with inherent resistance to inactivation by far ultraviolet radiation, near ultraviolet radiation, and thermal radiation. Virus with apparently increased resistance to inactivation by near ultraviolet radiation was isolated. Virus with increased resistance to far ultraviolet radiation was not obtained. No significant differences in response to thermal radiation were observed between wild virus and virus selected for increased resistance to inactivation by this agent. Repeated selection treatment with far ultraviolet radiation and with near ultraviolet radiation resulted in the production of virus with significantly reduced virulence in comparison with wild virus. The virulence of heat-selected virus did not differ from wild virus.     

Specificity and frequency of ultraviolet-induced reversion of an iso-1-cytochrome c ochre mutant in radiation-sensitive strains of yeast

The basis for the specific pattern of ultraviolet-induced reversion of cyc1-9, an ochre allele of the structural gene for iso-1-cytochrome c, has been examined in radiation-sensitive strains of yeast. Previous analysis, using RAD⁺ strains, showed that 21 out of 23 cyc1-9 revertants induced by ultraviolet light arose by A · T to G · C transition at the first position in the UAA codon, the remaining two occurring by A · T to T · A transversion at the second position (Stewart et al., 1972; Sherman &; Stewart, 1974). All possible base-pair substitutions could be obtained with the aid of other mutagens.It has now been shown that this specificity depends largely on the action of the RAD6 locus, since ultraviolet-induced revertants of cyc1-9 arose by a variety of base-pair substitutions in a strain carrying the rad6-1 allele. Induced reversion frequencies in strains carrying this allele are much lower than normal, though significantly higher than the spontaneous frequency, and the strains are more sensitive to the lethal effects of both ultraviolet and X-irradiation. The phenotypically similar rad18-2 mutation, which appears to block the same repair pathway as rad6-1, also has some effect on the reversion specificity, but its action depends on the presence of other, unidentified, mutations. Specificity was, however, completely unaltered in an excision-defective strain carrying the rad1-2 allele. Induced reversion frequency of cyc1-9 was much higher than normal in this strain. Photoreactivation studies indicated that pyrimidine dimers were responsible for most of the revertants in RAD+, rad1 and rad6 strains. These experiments show that the RAD6+ locus is intimately concerned with error-prone repair, and suggest that excision repair is substantially error-free.     

Motility and gravitactic orientation of the flagellate,Euglena gracilis,impaired by artificial and solar UV-B radiation

The effects of ultraviolet radiation on the gravitactic orientation of the freshwater flagellate,Euglena gracilis, were determined by a real time image analysis system. Both artificial UV radiation and solar radiation in a temperature-controlled growth chamber were employed. Histograms of gravitaxis showed that the degree of orientation decreased with increasing exposure time; this can be quantified using the Rayleigh test and upper quadrant summation. The effects of artificial UV radiation on the orientation are considerably stronger than those of solar radiation, probably because the radiation source emits higher fluence rates below 300 nm than found in solar radiation. The effects of monochromatic ultraviolet radiation on motility have been determined, and an action spectrum has been calculated.     

UVB Exposure of Farm Animals: Study on a Food-Based Strategy to Bridge the Gap between Current Vitamin D Intakes and Dietary Targets

Vitamin D deficiency is a global health problem. This study aimed to investigate the efficacy of ultraviolet (UV) B radiation for improving vitamin D₃ content of eggs and meat. In a two-factorial design hens that received diets with 0 (-D₃) or 3,000 IU (+D₃) vitamin D₃/kg were non-exposed (-UVB) or exposed to UVB radiation (+UVB) for 3 h daily over 4 weeks. Data show that UVB radiation was very effective in raising the vitamin D₃ content of egg yolk and meat. Egg yolk from +UVB/−D₃ hens had a higher vitamin D₃ content (17.5±7.2 µg/100 g dry matter (DM)) than those from the –UVB/+D₃ group (5.2±2.4 µg/100 g DM, p<0.01). Vitamin D₃ content in egg yolk of vitamin D₃-supplemented hens could be further increased by UVB radiation (32.4±10.9 µg/100 g DM). The content of 25-hydroxyvitamin D₃ (25(OH)D₃) in the egg yolk also increased in response to UVB, although less pronounced than vitamin D₃. Meat revealed about 4-fold higher vitamin D₃ contents in response to UVB than to dietary vitamin D₃ (p<0.001). In conclusion, exposure of hens to UVB is an efficient approach to provide consumers with vitamin D₃-enriched foods from animal sources.     

THE BACTERICIDAL EFFECT OF ULTRAVIOLET RADIATION ON ESCHERICHIA COLI IN LIQUID SUSPENSIONS

1. The irradiation of bacteria in liquid suspension has been made possible through: (a) the use of a specially balanced physiological salt solution which is practically non-absorbing for the wave lengths used, and which is of such composition that subsequent dilution of the bacterial suspension gives the proper number of organisms; (b) special design of the exposure cell and a very thorough method of stirring which subjects each organism equally to the radiation; (c) practically complete absorption of the incident radiation, through the use of very dense suspensions, thus eliminating the necessity for a separate determination of the absorption coefficients of the bacteria for the wave lengths used. 2. The method also provides a means for determining the effects of sub-lethal doses. 3. A formula is given for calculating from observed survival ratios the energy required to inactivate bacteria with ultraviolet radiation. The formula corrects for the protective action of non-viable organisms. 4. Data are given for the inactivation of 15 hour and 240 hour cultures of E. coli, washed and unwashed) and for 6–7 hour cultures, unwashed. These data are compared with those of other investigators. 5. A possible explanation for the differences in energy required to inactivate old, young, and standard cultures of bacteria is suggested. 6. The possible mechanism of the action of ultraviolet radiation on microorganisms is discussed.     

Resistivity of Spores to Ultraviolet and γ Radiation while Exposed to Ultrahigh Vacuum or at Atmospheric Pressure

Viability studies were conducted on microbial spores subjected to ultrahigh vacuum (UHV) in the 10^-9 to 10^-10 torr range. After 5 to 7 days in vacuum, they were exposed to ultraviolet (UV) or to γ radiation either while still under vacuum or in the presence of dried air. Among the four test organisms subjected to UHV and ultraviolet radiation, Aspergillus niger was the most resistant; Bacillus megaterium, B. subtilis var. niger, and B. stearothermophilus were about equally less resistant. All four spores were more sensitive to ultraviolet radiation when UHV-dried than when desiccant-dried. Of the four test organisms subjected to UHV and γ radiation, B. megaterium proved to be the most resistant; A. niger was the least resistant; and the remaining two organisms were of intermediate resistivity. All four organisms were less radiation resistant when UHV-dried than when irradiated in their normally hydrated state, and all showed an increased radiosensitivity after vacuum drying when oxygen was present. In addition, spores of B. subtilis var. niger and A. niger were less radiosensitive when UHV-dried and irradiated in vacuum than when “wet” and irradiated in air, whereas the reverse relationship was observed for the remaining two organisms. Based on the fact that microbial contaminants can be readily shielded from UV light by soils, metal particles, etc., and considering that the levels of ionizing radiations reported to be present in interstellar space are generally lower than those used in these experiments, the decrease in radioresistivity imparted by UHV drying is not of a sufficient magnitude to sterilize dependably portions of a spacecraft while on a mission.     

Mating type regulates the radiation-associated stimulation of reciprocal translocation events in Saccharomyces cerevisiae

Both ultraviolet (UV) and ionizing radiation were observed to stimulate mitotic, ectopic recombination between his3 recombinational substrates, generating reciprocal translocations in Saccharomyces cervisiae (yeast). The stimulation was greatest in diploid strains competent for sporulation and depends upon both the ploidy of the strain and heterozygosity at the MAT locus. The difference in levels of stimulation between MATa/MATα diploid and MATα haploid strains increases when cells are exposed to higher levels of UV radiation (sevenfold at 150 J/m²), whereas when cells are exposed to higher levels of ionizing radiation (23.4 krad), only a twofold difference is observed. When the MATα gene was introduced by DNA transformation into a MATa/matα::LEU2 ⁺ diploid, the levels of radiation-induced ectopic recombination approach those obtained in a strain that is heterozygous at MAT. Conversely, when the MATA gene was introduced by DNA transformation into a MATα haploid, no enhanced stimulation of ectopic recombination was observed when cells were irradiated with ionizing radiation but a threefold enhancement was observed when cells were irradiated with UV The increase in radiation-stimulated ectopic recombination resulting from heterozygosity at MAT correlated with greater spontaneous ectopic recombination and higher levels of viability after irradiation. We suggest that MAT functions that have been previously shown to control the level of mitotic, allelic recombination (homolog recombination) also control the level of mitotic, radiation-stimulated ectopic recombination between short dispersed repetitive sequences on non-homologous chromosomes.     

Electrophysiological Properties of Cells in the Median Ocellus of Limulus

Two types of photoreceptors are found in the median ocellus of Limulus. One type is maximally sensitive to ultraviolet (UV) light, the other to green light; they are called UV and VIS cells, respectively. Biphasic receptor potentials, consisting of a small initial hyperpolarizing phase and a later slow depolarizing phase, can be recorded from both receptor types. These biphasic responses are elicited in UV cells in response to long-wavelength light, and in VIS cells in response to ultraviolet light. Another type of hyperpolarizing response can be recorded in UV cells: after a bright ultraviolet stimulus, the cell remains depolarized; long-wavelength light rapidly returns the membrane potential to its value preceding ultraviolet illumination (this long-wavelength-induced potential change is called a "repolarizing response"). Also, a long-wavelength stimulus superimposed during a UV stimulus elicits a sustained repolarizing response. A third cell type (arhabdomeric cell) found in the median ocellus generates large action potentials and is maximally sensitive to UV light. Biphasic responses and repolarizing responses also can be recorded from arhabdomeric cells. The retina is divided into groups of cells; both UV cells and VIS cells can occur in the same group. UV cells in the same group are electrically coupled to one another and to an arhabdomeric cell.     

Comparison of the reversibility of locipet23 andlys2 after UV irradiation in the standard and UV-sensitive strains ofSaccharomyces cerevisiae

Reversibility of the respiration-deficient locuspet23 and auxotrophic locuslys2 was followed in the standard (RAD1) and UV sensitive (rad1–2) strains ofSaccharomyces cerevisiae, both after identical doses of UV radiation and at identical survival. When comparing the reversibility after the treatment with identical doses of UV radiation a much higher reversibility of both loci in strainrad1–2 could be detected. When comparing the reversibility of the loci in question at identical survival of both strains it could be found that the reversibility of thepet23 locus is again much higher in strainrad1–2, whereas the reversibility of thelys2 locus is roughly identical in the two strains. Thus, the function of geneRAD1 in repair processes is apparently associated with the “error-free” repair, both at low and high doses of ultraviolet radiation.     

Interconversion of Yeast Mating Types II. Restoration of Mating Ability to Sterile Mutants in Homothallic and Heterothallic Strains

The two mating types of the yeast Saccharomyces cerevisiae can be interconverted in both homothallic and heterothallic strains. Previous work indicates that all yeast cells contain the information to be both a and α and that the HO gene (in homothallic strains) promotes a change in mating type by causing a change at the mating type locus itself. In both heterothallic and homothallic strains, a defective α mating type locus can be converted to a functional a locus and subsequently to a functional α locus. In contrast, action of the HO gene does not restore mating ability to a strain defective in another gene for mating which is not at the mating type locus. These observations indicate that a yeast cell contains an additional copy (or copies) of α information, and lead to the "cassette" model for mating type interconversion. In this model, HMa and hmα loci are blocs of unexpressed α regulatory information, and HMα and hma loci are blocs of unexpressed a regulatory information. These blocs are silent because they lack an essential site for expression, and become active upon insertion of this information (or a copy of the information) into the mating type locus by action of the HO gene.     

The fate of thymine-containing dimers in ultraviolet-irradiated Halobacterium cutirubrum

Extremely halophilic bacteria do not recover in the dark from the effects of ultraviolet radiation, although they can be completely photoreactivated, thus proving that pyrimidine dimers are the cytotoxic photoproducts. We have now shown, by studying the fate of thymine-containing dimers during dark liquid-holding of Halobacterium cutirubrum, that the lack of dark repair in these bacteria is due to their inability to excise such lesions, in contrast to Escherichia coli B. Nevertheless, extensive nonspecific degradation of DNA occurs in H. cutirubrum following ultraviolet irradiation, so the lack of dimer excision is not due to a generalised inability to degrade DNA after such treatment. These findings raise interesting questions concerning the basis of the resistance of halophiles to ultraviolet radiation.     

Modifying effects of ultraviolet irradiation on the development of abnormal body patterns in centrifuged insect embryos (Smittia sp., Chironomidae,Diptera)

In Smittia and other chironomid embryos, both anterior and posterior egg halves can give rise to either anterior or posterior segments. Upon various types of experimental interference, eggs may develop one of four basic body patterns: normal embryos, double cephalons, double abdomens, or inverted embryos. From a previous model of anteroposterior determination, we derive four sets of predictions for the results of combined ultraviolet irradiation and centrifugation experiments. While most of the actual results are in agreement with the predictions, some are not. Most of the discrepancies are resolved in a modified version of the model. According to the new model, anterior and posterior egg halves contain both anterior and posterior cytoplasmic determinants. These are thought to be mutually repressive, and to control an overall determination for either anterior or posterior development. Centrifugation and ultraviolet irradiation appear to affect the relative strength of anterior determinants in one or both of the egg halves, thus modifying the probabilities for the four basic body patterns to develop. Different frequencies of these patterns, which have been obtained after similar experimental treatment of different chironomid species, can be ascribed to species-specific variation in the ultraviolet sensitivity of anterior and posterior determinants.     

On the Components of Segregation Distortion in DROSOPHILA MELANOGASTER. II. Deletion Mapping and Dosage Analysis of the SD Locus

Segregation distorter (SD) chromosomes are preferentially transmitted to offspring from heterozygous SD/SD⁺ males owing to the induced dysfunction of the SD⁺-bearing sperm. This phenomenon involves at least two major loci: the Sd locus whose presence is necessary for distortion to occur and the Rsp locus which acts as the site of Sd action. Several additional loci on SD chromosomes enhance distortion.—In a previous study deletions were used to map the Sd locus and to determine some of its properties. We have extended this analysis with the isolation and characterization of 14 new deletions in the Sd region. From our results we conclude (1) SD chromosomes contain a single Sd locus located in region 37D2-6 of the salivary gland chromosome map. Deletion of this locus in any of three SD chromosomes now studied results in complete loss of ability to distort a sensitive chromosome; (2) the reduced male fecundity observed in many homozygous SD or SD_i/SD_j combinations is due at least in part to the action of the Sd locus. The fecundity of these males can be substantially increased by deletion of one Sd locus. Thus, it is the presence of two doses of Sd rather than the absence of Sd⁺ that produces the lowered male fecundity in SD homozygotes; (3) Sd behaves as a neomorph, whereas Sd⁺, if it exists at all, is amorphic with respect to segregation distortion; (4) these results support a model in which the Sd product is made in limiting amounts and the interaction of this product with the Rsp locus causes sperm dysfunction. The Sd product appears to act preferentially at Rsp^s (sensitive-Responder) but may also act at Rspⁱ (insensitive-Responder).     

Potential contributions of antimutator activity to the metastasis suppressor function of NM23-H1

nm23-h1 is a well-documented metastasis suppressor gene whose mechanism(s) of action have yet to be fully elucidated. The purpose of this report is to discuss recent advances in investigating the potential role of a novel 3′–5′ exonuclease activity identified recently in our laboratory, a biochemical function associated, in general, with DNA repair and replication. We have employed a site-directed mutagenesis approach to demonstrate that the 3′–5′ exonuclease activity of NM23-H1 is required for its metastasis suppressor function. Consistent with a role in DNA repair, we also observe that the single yeast NM23 homolog (YNK1) is required for the maintenance of genomic integrity and normal kinetics of DNA repair in response to exposure to ultraviolet radiation. These results and their implications for understanding the molecular mechanisms underlying NM23-H1 functions in cancer are discussed.     

Retardation of Regeneration and Division of Blepharisma by Ultraviolet Radiation and Its Photoreversal

Regeneration of Blepharisma undulans variety japonicus from which the hypostome has been removed is retarded by dosages of 3000 to 4600 ergs/mm.² at wavelength 2654A most strongly when the fragment is exposed soon after cutting. Dosages greater than 4600 ergs/mm.² prevent regeneration. Regeneration is also retarded strongly when the Blepharisma are cut soon after irradiation. Starvation retards regeneration and potentiates the effect of ultraviolet radiations. Division after regeneration of Blepharisma is also retarded by ultraviolet radiations about equally, regardless of when the Blepharisma are cut indicating a more lasting effect of the radiations upon the cells. Blepharisma cut after irradiation usually recover from the effects of the radiations sooner than uncut individuals given the same dosage. Retardation of division by ultraviolet radiation is subject to photoreversal by visible light, especially in a nitrogen atmosphere, provided the ultraviolet dose is not excessive. Visible light alone if prolonged, retards regeneration or may even kill the cut fragments of Blepharisma.