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At least 307 records · Page 17Linked to original sources
PubMed1993

Mutation induction by UV light in retroviral hprt cDNA integrated at various chromosomal positions in repair-deficient hamster cells.

Mutation induction by UV irradiation was studied in a retroviral vector integrated in one copy per cell at various chromosomal positions. As a mutational target, hamster hprt cDNA was present on the retroviral vector. To minimize the influence of repair we used repair-deficient hamster cells, V-H1 and UV5, as a recipient for the vector. There is no major influence of chromosomal position on UV-induced mutation frequency and spectrum because no statistically significant difference between mutation induction in retroviral cDNA copies integrated at different chromosomal sites was observed. However, a major difference was found in mutation induction between the endogenous hamster hprt gene and the retroviral cDNA copies. Most noticeable was the absence in the cDNA of the strong strand bias for mutation induction, which was reported for the endogenous hprt gene. Our results with the hprt cDNA exclude as a general phenomenon a difference in mutation induction for leading and lagging strand DNA replication, which was proposed as an explanation for this strand bias in the endogenous gene. The similarity of mutation induction in the different retroviral cDNA copies, all directly surrounded by the same DNA sequence elements, together with the marked difference between the mutation induction in the endogenous gene and the cDNA copies may point to an important role of chromatin structure in mutation induction.

Animals↗
PubMed1976

Prophage induction and inactivation by UV light.

Analysis of the induction curves for UV light-irradiated Haemophilus influenzae lysogens and the distribution of pyrimidine dimers in a repair-deficient lysogen suggests that one dimer per prophage-size segment of the host bacterial chromosome is necessary as a preinduction event. The close correlations obtained prompted a renewed consideration of the possibility that direct prophage induction occurs when one dimer is stabilized within the prophage genome. The host excision-repair system apparently functions to reduce the probability of "stabilizing" within the prophage those dimers that are necessary for induction and inactivation. The presence of the inducible defective prophage in strain Rd depresses the inducibility of prophage HP1c1.

Bacteriophages↗
PubMed1975

[Application of animal mass psychology to pharmacology (XI). The role of light in the induction of convulsions in E1-mice].

In preliminary experiments to investigate the influence of masking the eyes of E1-mice on the rate of non-convulsions (RNC), it was suggested that the quantity of light as well as visibility itself played a role in inducing convulsions. The following experiments were thus carried out: (a) Both TSC (the threshold of number of shakings required for induction of convulsions) and RNC increased remarkably on the 5th day after enucleation of bilateral eyeballs from E1-mice, but 15 days later recovery to control level was observed. Moreover, TSC and RNC at 2 p.m. increased considerably compared with the control, however, the increase was rarely observed at 10 a.m.. (b) 2 groups of E1-mice reared intact under radiation of light plus different time schedules were shaken at 10 a.m. and 2 p.m., respectively. Consequently, TSC after radiation for 5 hours was less than that after radiation for 1 hour. When observed 9 hr after radiation, TSC could not be differentiated from TSC at 5 hr after the radiation. (c) E1-mice were reared under continuous lighting, continuous darkness or a normal lighting situation, after which TSC and RNC were examined. From our observations, the intensity of light appears to play a role in inducing convulsions. (d) When mice were shaken immediately after lighting, RNC decreased in inverse proportion to increase in the quantity of light. TSC was not influenced by the luminosity itself. One hour after lighting, however, the influence of lighting had disappeared. The intensity, quantity or irradiation time would not, however, influence the induction of E1-mice convulsions so much as the cognizance of light by the individual animals. Such a conception is derived from the "cognitive theory" in psychology.

Animals↗
PubMed1988

The role of nitrate and ammonium ions and light on the induction of nitrate reductase in maize leaves.

Corn seedlings (Zea mays cv W64A x W182E) were grown hydroponically, in the presence or absence of NO(3) (-), with or without light and with NH(4)Cl as the only N source. In agreement with earlier results nitrate reductase (NR) activity was found only in plants treated with both light and NO(3) (-). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by transfer of the proteins to nitrocellulose paper and reaction with antibodies prepared against a pure NR showed that crude extracts prepared from light-grown plants had a polypeptide of approximately 116 kilodaltons (the subunit size for NR) when NO(3) (-) was present in the growth medium. Crude extracts from plants grown in the dark did not have the 116 kilodalton polypeptide, although smaller polypeptides, which reacted with NR-immunoglobulin G, were sometimes found at the gel front. When seedlings were grown on Kimpack paper or well washed sand, NR activity was again found only when the seedlings were exposed to light and NO(3) (-). Under these conditions, however, a protein of about 116 kilodaltons, which reacted with the NR antibody was present in light-grown plants whether NO(3) (-) was added to the system or not. The NR antibody cross-reacting protein was also seen in hydroponically grown plants when NH(4)Cl(-) was the only added form of nitrogen. These results indicate that the induction of an inactive NR-protein precursor in corn is mediated either by extremely low levels of NO(3) (-) or by some other unidentified factor, and that higher levels of NO(3) (-) are necessary for converting the inactive NR cross-reacting protein to a form of the enzyme capable of reducing NO(3) (-) to NO(2) (-).

Journal Article↗
PubMed1984

Induction by UV light of the SOS function sfiA in Escherichia coli strains deficient or proficient in excision repair.

The influence of the nucleotide excision repair system on the induction by UV irradiation of the SOS function sfiA has been investigated. The level of sfiA expression was monitored by means of a sfiA::lacZ operon fusion in both the wild-type strain and a uvrA mutant. We found that the initial steady rate of sfiA expression was proportional to the UV dose and was identical in uvr+ and uvrA backgrounds. This suggests that the initial steady rate of sfiA expression is determined by the initial number of lesions and before any effect of excision repair. We confirmed that after 2 h of expression the net synthesis of sfiA product is, for the same UV dose, about five times lower in uvr+ than in uvrA strains. We show that this is due to earlier repression of the SOS system in uvr+ than in uvrA strains and not to different initial rates.

DNA Repair↗
PubMed1983

Heat-shock induction of ultraviolet light resistance in Saccharomyces cerevisiae.

When exponentially growing diploid wild type Saccharomyces cerevisiae cells were subjected to a sudden rise in temperature (heat shock) they responded by increasing their resistance to the lethal effects of ultraviolet light. We have previously reported heat shock-induced increases in heat and ionizing radiation resistance. The shock-induced rise in resistance to uv light reported here was examined in terms of DNA repair capacity, and we find that the increase is due to induction of the recombinational repair system with no significant response from the uv-excision repair process.

Diploidy↗
PubMed1996

Apoptosis induction of ultraviolet light A and photochemotherapy in cutaneous T-cell Lymphoma: relevance to mechanism of therapeutic action.

The anti-tumor action of many chemotherapeutic agents has recently been attributed to the induction of apoptosis in the malignant cell population. In this study, we investigated the ability of extracorporeal photopheresis (ExP) and in vitro PUVA (8-methoxy-psoralen + ultraviolet A) therapy to induce apoptosis in peripheral blood mononuclear cells from Sezary syndrome patients and normal controls. Flow cytometric analysis of ExP- or PUVA-treated peripheral blood lymphocytes demonstrated two distinct cell populations within 24 h of treatment. One population was similar to untreated controls with the other exhibiting characteristics of apoptotic cell death, i.e., a loss of cell volume and an accompanying increase in cell density. This latter population was comprised of cells with DNA strand breaks as determined by the Tdt-mediated deoxyuridine triphosphate-biotin nick end labeling assay. Apoptosis was also confirmed morphologically by fluorescent and electron microscopy as well as by demonstration of characteristic DNA strand breaks (laddering) using gel electrophoresis. Apoptosis was not observed with 8-methoxypsoralen (< or = 300 ng per ml) alone; however, ultraviolet A alone at doses > or = 2 J per cm2 induced apoptosis in lymphocytes. Peripheral blood T-cell subpopulations of Sezary syndrome patients, including the malignant clone, were equally susceptible to apoptosis subsequent to either photopheresis or PUVA treatment. In contrast, monocytes (CD14+/CD45+) appear to be resistant to apoptosis induction by ExP or PUVA treatment. Moreover, ExP-treated and untreated monocytes phagocytized apoptotic, but not untreated, peripheral blood mononuclear cells. ExP and PUVA have been shown to be efficacious and well-tolerated therapies in the treatment of dermatologic diseases and transplant rejection. These data suggest that induction of apoptosis may be an important event for therapeutic efficacy.

Apoptosis↗
PubMed2004

Efficacy of different UV-emitting light sources in the induction of T-cell apoptosis.

Ultraviolet B (UV-B) radiation is a modality widely used for the treatment of different skin diseases. One of the major mechanisms of UV-B immunosuppression in this treatment modality is thought to be an apoptosis-inducing effect on T cells infiltrating the skin. We examined the T-cell apoptosis-induction capacities of four different UV light sources, with and without UV filters. The xenon chloride (XeCl) laser proved to be the strongest apoptosis inducer. The use of a phtalic acid filter eliminated UV radiation almost completely below 300 nm, which resulted in a severe decrease in the apoptosis-inducing capacity of different UV-B sources. Using the results of the measurements with polychromatic UV light sources, the wavelength dependence of UV-B light for the induction of T-cell apoptosis was also determined. The regression line of the action spectrum demonstrated a continuous decrease from 290 to 311 nm. The apoptosis-inducing capacity of the XeCl laser was almost four times higher than the calculated value according to the action spectrum, which might be attributed to the high irradiance of the laser as compared with nonlaser light sources.

Apoptosis↗
PubMed2004

Dissipation of excess energy triggered by blue light in cyanobacteria with CP43' (isiA).

The chlorophyll-protein CP43' (isiA gene) induced by stress conditions in cyanobacteria is shown to serve as an antenna for Photosystem II (PSII), in addition to its known role as an antenna for Photosystem I (PSI). At high light intensity, this antenna is converted to an efficient trap for chlorophyll excitations that protects system II from photo-inhibition. In contrast to the 'energy-dependent non-photochemical quenching' (NPQ) in chloroplasts, this photoprotective energy dissipation in cyanobacteria is triggered by blue light. The induction is proportional to light intensity. Induction and decay of the quenching exhibit the same large temperature-dependence.

Adaptation, Physiological↗
PubMed1986

Sensitivity to DNA-damaging agents and mutation induction by UV light in UV-sensitive CHO cells.

Three UV-sensitive (UVs) mutants isolated from a CHO cell line were analyzed for survival after exposure to H2O2, EMS, MMC, CCNU, X-rays and for mutation induction after UV-irradiation. The UVs mutants showed normal sensitivities to EMS and H2O2, whereas they were hypersensitive to the bifunctional alkylating agents MMC and CCNU and to hypoxic X-irradiation. Compared to parental cells, one of the UV-sensitive clones showed approximately 3- and 7-fold enhancement in the mutagenic response per unit UV dose for 6-thioguanine and ouabain resistance, respectively.

Animals↗
PubMed2002

Expression of the grape dihydroflavonol reductase gene and analysis of its promoter region.

Dihydroflavonol reductase (DFR) is a key enzyme involved in anthocyanin biosynthesis and proanthocyanidin synthesis in grape. DFR catalyses the reduction of dihydroflavonols to leucoanthocyanidins in the anthocyanin pathway. The DFR products, the leucoanthocyanidins, are substrates for the next step in the anthocyanin pathway and are also the substrates for the proanthocyanidin pathway. In the present study the promoter of the grape dfr gene was cloned. Analysis of the dfr promoter sequence revealed the existence of several putative DNA binding motifs. The dfr promoter was fused to the uidA gene and the control of this fusion and the endogenous dfr gene expression, was studied in transformed plants and in red cell suspension originated from fruits. The dfr promoter-uidA gene fusion was expressed in leaves, roots and stems. Deletions of the dfr promoter influenced the specificity of the expression of the GUS gene fusion in plantlet roots and the level of expression in plants and in the red cell suspension originated from fruits. The deletion analysis of the dfr promoter suggests that a specific sequence located between -725 to -233 might be involved in expression of the dfr gene in fruits. Light, calcium and sucrose induced the dfr gene expression. In the transformed suspension cultures, expression of both the endogenous dfr gene and the dfr promoter-uidA gene fusions was induced by white light. The induction by both light and calcium suggests the possible involvement of a UV receptors signal transduction pathway in the induction of the dfr gene. The induction of the dfr gene and the dfr promoter-uidA gene fusions by light and sucrose indicates a close interaction between sucrose and light signalling pathways.

Alcohol Oxidoreductases↗
PubMed1982

Induction of myosin light chain synthesis in heterokaryons between normal diploid cells.

Quail myoblasts were maintained in an undifferentiated state by first blocking differentiation with 5-bromodeoxyuridine and then reversing the block in the presence of phorbol-12-myristate-13-acetate. The synthesis of quail skeletal myosin light chain 1 is induced in heterokaryons formed by fusing these undifferentiated quail myoblasts to differentiated chick myocytes. These results extend observations previously obtained using an established line of rat myoblasts and indicate that the induction is a result of regulatory interactions present in normal diploid cells.

Animals↗
PubMed1992

Light Moderates the Induction of Phosphoenolpyruvate Carboxylase by NaCl and Abscisic Acid in Mesembryanthemum crystallinum.

In Mesembryanthemum crystallinum, phosphoenolpyruvate carboxylase is synthesized de novo in response to osmotic stress, as part of the switch from C(3)-photosynthesis to Crassulacean acid metabolism. To better understand the environmental signals involved in this pathway, we have investigated the effects of light on the induced expression of phosphoenolpyruvate carboxylase mRNA and protein in response to stress by 400 millimolar NaCl or 10 micromolar abscisic acid in hydroponically grown plants. When plants were grown in high-intensity fluorescent or incandescent light (850 microeinsteins per square meter per second), NaCl and abscisic acid induced approximately an eightfold accumulation of phosphoenolpyruvate carboxylase mRNA when compared to untreated controls. Levels of phosphoenolpyruvate carboxylase protein were high in these abscisic acid- and NaCl-treated plants, and detectable in the unstressed control. Growth in high-intensity incandescent (red) light resulted in approximately twofold higher levels of phosphoenolpyruvate carboxylase mRNA in the untreated plants when compared to control plants grown in high-intensity fluorescent light. In low light (300 microeinsteins per square meter per second fluorescent), only NaCl induced mRNA levels significantly above the untreated controls. Low light grown abscisic acid- and NaCl-treated plants contained a small amount of phosphoenolpyruvate carboxylase protein, whereas the (untreated) control plants did not contain detectable amounts of phosphoenolpyruvate carboxylase. Environmental stimuli, such as light and osmotic stress, exert a combined effect on gene expression in this facultative halophyte.

Journal Article↗
PubMed1977

Kinetics of mutation induction by ultraviolet light in excision-deficient yeast.

We have measured the frequency of UV-induced reversions (locus plus suppressor) for the ochre alleles ade2-1 and lys2-1 and forward mutations (ade2 adex double auxotrophs) in an excision-deficient strain of Saccharomyces cerevisiae (rad2-20). For very low UV doses, both mutational systems exhibit linear induction kinetics. However, as the dose increases, a strikingly different response is observed: in the selective reversion system a transition to higher order induction kinetics occurs near 9 ergs/mm2 (25% survival), whereas in the nonselective forward system the mutation frequency passes through a maximum near 14 ergs/mm2 (4.4% survival) and then declines. This contrast in kinetics cannot be explained in any straightforward way by current models of induced mutagenesis, which have been developed primarily on the basis of bacterial data. The bacterial models are designed to accommodate the quadratic induction kinetics that are frequently observed in these systems. We have derived a mathematical expression for mutation frequency that enables us to fit both the forward and reversion data on the assumptions that mutagenesis is basically a "single event" Poisson process, and that mutation and killing are not necessarily independent of one another. In particular, the dose-response relations are consistent with the idea that the sensitivity of the revertants is about 25% less than that of the original cell population, whereas the sensitivity of the forward mutants is about 29% greater than the population average. We argue that this relatively small differential sensitivity of mutant and nonmutant cells is associated with events that take place during mutation expression and clonal growth.

Chromosome Mapping↗
PubMed2002

White Collar-1, a circadian blue light photoreceptor, binding to the frequency promoter.

In the fungus Neurospora crassa, the blue light photoreceptor(s) and signaling pathway(s) have not been identified. We examined light signaling by exploiting the light sensitivity of the Neurospora biological clock, specifically the rapid induction by light of the clock component frequency (frq). Light induction of frq is transcriptionally controlled and requires two cis-acting elements (LREs) in the frq promoter. Both LREs are bound by a White Collar-1 (WC-1)/White Collar-2 (WC-2)-containing complex (WCC), and light causes decreased mobility of the WCC bound to the LREs. The use of in vitro-translated WC-1 and WC-2 confirmed that WC-1, with flavin adenine dinucleotide as a cofactor, is the blue light photoreceptor that mediates light input to the circadian system through direct binding (with WC-2) to the frq promoter.

Circadian Rhythm↗