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D Frankenberg

Publications and source records attributed to D Frankenberg.

At least 37 records · Page 2Linked to original sources
PubMed1994

Radiation-induced mitotic gene conversion frequency in yeast is modulated by the conditions allowing DNA double-strand break repair.

Repair of DNA double-strand breaks (DSB) involves recombinational processes which may lead to gene conversion (intragenic recombination). Using the diploid yeast mutant rad54-3 heteroallelic for his1 (his1-7/his1-1) and temperature conditional for DSB rejoining, radiation induced gene conversion was investigated as dependent on DSB repair under different postirradiation conditions. Gene conversion is negligible under conditions preventing DSB repair (36 degrees C). In contrast, gene conversion is observed when cells are incubated at the permissive temperature (23 degrees C) both under growth and nongrowth conditions. However, there is a much higher yield of convertants for cells incubated under growth as opposed to nongrowth conditions. These results can most plausibly be explained by the cell cycle regulated enhancement of the expression of genes such as PMS and POL3 known to be involved in gene conversion processes and/or the enhanced recombination in transcriptionally active genes. 'Nutrient stress' inducible responses and/or cell cycle specific recombination pathways leading to gene conversion events preferentially in S-phase cells seem to be less likely.

Cell Survival↗
PubMed1994

Simple and complex double-strand breaks induced by electrons.

Biophysical modelling of DNA damage based on Monte Carlo simulation of charged particle tracks allows to describe radiation induced double-strand breaks (dsb) in a quantitative and qualitative way. Experimental and calculated data suggest that in the electron energy range from 50 eV to 1 MeV dsb can be grouped in simple and complex dsb. Complex dsb are mainly produced by low energy electrons with initial energies between approximately 200 and approximately 500 eV, whereas simple dsb are preferentially induced by energy transfers < 200 eV, which produce at least two ionizations.

DNA Damage↗
PubMed1994

Half-life values for DNA double-strand break rejoining in yeast can vary by more than an order of magnitude depending on the irradiation conditions.

Yeast cells in stationary phase were exposed under oxic or anoxic conditions to sparsely (30 MeV electrons) or densely (3.5 MeV alpha-particles) ionizing radiation. For all four experimental set-ups postirradiation treatment of cells was the same, i.e. cells were kept under oxic conditions in non-growth medium at 30 degrees C. Double-strand break (dsb) rejoining was measured during this treatment yielding the following results: (1) half-life values ranged from < 60 min (electrons, anoxia) to 3.8 h (low doses of electrons, oxia), 7 h (alpha-particles, anoxia), 10 h (high doses of electrons, oxia) and 13 h (alpha-particles, oxia). (2) In the case of exposure of oxic cells to electrons a biphasic rejoining kinetics is observed with a dose-dependent increase of the fraction of the slow component. These results suggest that half-life values of dsb rejoining in a given cell depend on physical, chemical and biological parameters. The rejoining of dsb slows down with increasing LET, being probably due to the increasing complexity of dsb. Oxygenation of cells at the time of irradiation affects half-life values, indicating that radiation chemistry plays an important role. The biphasic rejoining kinetics observed for dsb induced by electrons in oxic cells is interpreted in terms of a dose-dependent change of chromatin structure hindering the interaction between damaged chromatin and the rejoining enzymes rather than by two chemically distinct types of dsb with differing half-life values.

Alpha Particles↗
PubMed1994

Survival curves with shoulders: damage interaction, unsaturated but dose-dependent rejoining kinetics or inducible repair of DNA double-strand breaks?

Double-strand breaks (DSBs) are considered as critical lesions for radiation-induced cell killing. Two processes, identified by the rejoining kinetics of DNA DSBs induced in yeast at radiation doses which are also applied in survival studies, can lead to survival curves with shoulders: firstly, "DSB interaction" when repair time is unrestricted, and secondly, a biphasic and unsaturated DSB rejoining, where the fractions of the two rejoining components are dose-dependent and repair time is restricted. Thus the unsaturated rejoining kinetics of DSBs is not in contradiction to the observation of survival curves with shoulders. While these two mechanisms are derived from studies on cells kept under nongrowth conditions during postirradiation incubation, experiments are reviewed which were designed to study inducibility of DSB rejoining. Some of these studies suggest that rejoining of DSBs under growth conditions may include an inducible process.

Animals↗
PubMed1993

Mechanisms of oxygen radiosensitization in irradiated yeast. I. DNA double-strand breakage.

The relative contributions of the OH-mediated and direct radiation effect on the induction of DNA double-strand breaks (dsbs) were evaluated in two haploid yeast cell lines (GSH+ and gsh-) irradiated under oxic or hypoxic conditions in the absence or presence of 6 M glycerol as an OH radical scavenger. Gsh- cells are deficient in glutathione (GSH) biosynthesis, their GSH content is only 2% compared with GSH+ cells. Similar relative contributions are observed for both cell lines. Under oxic irradiation conditions about 64% of the response can be attributed to the OH-mediated (or indirect) radiation effect, whereas in hypoxic cells the indirect effect is only about 45%. High oxygen enhancement ratios (OERs) are observed for the OH-mediated radiation effect (4.24 for GSH+, 2.70 for gsh- cells) and low OERs for the direct effect (1.66 for GSH+, 1.44 for gsh- cells). The weighted total (i.e. direct and indirect) OER is 2.74 (GSH+) and 2.03 (gsh-). The dependence of radiosensitization for double-strand breakage on oxygen concentration is characterized by three components whose K-values are 0.5, 4 and 20% oxygen for GSH+ cells and 0.45, 5 and 60% oxygen for gsh- cells. Evidence is presented that the first two components represent the radiosensitization by oxygen of the OH-mediated effect, whereas the third component, requiring the highest oxygen concentration for sensitization, represents the radiosensitization by the direct effect. GSH+ and gsh- cells show virtually the same K-values for the OH-mediated effect, but different K-values for the direct effect.

DNA Damage↗
PubMed1992

2-deoxy-D-glucose inhibits rejoining of radiation-induced DNA double-strand breaks in yeast.

Effects of 2-deoxy-D-glucose (2-DG) on radiation-induced DNA double-strand breaks (dsb) have been studied under non-growth conditions in a respiratory-deficient strain of the yeast Saccharomyces cerevisiae. Velocity sedimentation in neutral sucrose gradients was used to measure DNA dsb. Addition of 2-DG to the liquid-holding medium (67 mM phosphate buffer, pH 5, 30 degrees C) at an equimolar concentration with glucose (50 mM) reduced the rate and extent of dsb rejoining. The inhibition of rejoining mediated by 2-DG is reversible for the majority--but not all--of the radiation-induced dsb.

DNA↗
PubMed1992

Heavy ion-induced DNA double-strand breaks in yeast.

DNA double-strand break (dsb) induction in diploid yeast was measured by neutral sucrose sedimentation after exposure to very heavy ions with values of linear energy transfer (LET) ranging from about 300 to 11500 ke V/microns. Linear fluence dependencies were found in all cases from which dsb production cross-sections (sigma dsb) could be calculated. Corresponding cross-sections for cell killing (sigma i) were derived from final slopes of survival curves measured in parallel and for the same fluence range. A close correlation was found between sigma i and sigma dsb. It is calculated that over the entire LET range, including 30 MeV electron irradiation, about 22 dsb are induced per lethal event when high exposures are considered.

Acceleration↗
PubMed1991

Different oxygen enhancement ratios for induced and unrejoined DNA double-strand breaks in eukaryotic cells.

DNA double-strand breaks (DSBs) are 2.9 times more frequently induced in yeast cells exposed to sparsely ionizing 30-MeV electrons under oxic compared to anoxic conditions. The rejoining of DSBs induced under anoxic conditions was investigated under conditions allowing repair of potentially lethal damage and compared to the rejoining of DSBs induced in oxic cells. In contrast to the biphasic rejoining kinetics of DSBs induced in oxic cells, the rejoining kinetics of DSBs induced in anoxic cells is complicated by the formation of secondary DSBs. These arise during postirradiation incubation of cells, presumably as a consequence of repair processes acting on radiation-induced lesions other than DSBs. These secondary DSBs may at least partially explain the finding that a greater fraction of unrejoinable DSBs is present in cells irradiated under anoxic compared to oxic conditions. As a consequence, the oxygen enhancement ratio of the yield of the remaining DSBs is decreasing in the course of DSB rejoining.

Cell Hypoxia↗
PubMed1990

A comparative study of rejoining of DNA double-strand breaks in yeast irradiated with 3.5 MeV alpha-particles or with 30 MeV electrons.

Yeast cells were irradiated with 3.5 MeV alpha-particles and 30 MeV electrons, as reference radiation. The kinetics of DNA double-strand break (dsb) rejoining during incubation of cells under non-growth conditions (PLDR conditions) were measured using the neutral sedimentation technique. A monophasic kinetic was found after irradiation of cells with alpha-particles, with a dose-independent t1/2 value of about 13 h. The kinetics of rejoining of dsb induced by 30 MeV electrons was found to be biphasic, with dose-independent t1/2 values of 3.8 h for the initial and of about 11 h for the slow component. The fraction of the slow component was, however, dose-dependent. These kinetics were measured for both types of radiation at doses yielding high surviving fractions (5% up to 100%). Dsb are induced linearly with dose of both radiations. The RBE value of alpha-particles was found to be 2.5 for initial dsb. The RBE of alpha-particles increased as a consequence of dsb rejoining. This increase in RBE value suggests that DSB may be primary lesions for chromosome aberrations, cellular inactivation and oncogenic transformation of mammalian cells which all exhibit high RBE values of alpha-particles.

Alpha Particles↗
PubMed1990

DNA double-strand breaks: their repair and relationship to cell killing in yeast.

Yeast is a suitable eukaryotic organism in which to study DNA double-strand breakage measured by the neutral sucrose gradient sedimentation technique and cell killing in the same range dose of sparsely ionizing radiations. Radiosensitive mutants (including temperature conditional ones) exist in which rejoining of double-strand breaks (dsb) is not detectable. In such mutants approximately one dsb per cell corresponds to a lethal event, suggesting that a dsb is a potentially lethal lesion. There are two modes by which dsb may confer cell lethality: firstly, an unrepaired dsb may be lethal on its own and secondly, two dsb may interact to form a lethal lesion (binary misrepair). The operationally defined cellular phenomena of potentially lethal damage (PLD) repair and sublethal damage (SLD) repair are both based on the repair of dsb. Induced dsb show a linear and unrejoined dsb a linear-quadratic relationship with dose. At low dose rate the quadratic component is abolished in accordance with the exponential survival curve observed. The dose-rate effect is based on dsb repair during irradiation; it is absent in dsb repair-deficient mutants.

Cell Survival↗
PubMed1990

Fast kinetics of the oxygen effect for DNA double-strand breakage and cell killing in irradiated yeast.

Lifetimes of oxygen-dependent precursors of DNA double-strand breaks (dsb), as determined by applying the gas explosion technique, were found to be dose-dependent. The analysis of data for dsb induction obtained in diploid 211*B cells by the neutral sucrose sedimentation technique exhibits a half-life of 2.18 ms at a pulse dose of 500 Gy. Lifetimes are also obtained indirectly by analysing the inactivation of diploid rad54-3 cells, which are defective in the rejoining of dsb when incubated at 36 degrees C. The half-life at a pulse dose of 40 Gy is only 0.25 ms. Since the cell size of both strains is very similar, the nine-fold longer lifetime determined in cells of strain 211*B may be caused by radiolytic depletion of glutathione due to the 12-fold higher dose applied to these cells. Therefore, the lifetime measured by the inactivation of rad54-3 cells (36 degrees C) is considered to be more relevant than that obtained by direct measurements of dsb. The influence of dsb rejoining on the fast kinetics of the oxygen effect was studied using rad54-3 cells, which are capable of rejoining dsb when incubated at 23 degrees C. When allowance for dsb rejoining was made, two components become detectable with half-lives of 0.75 and 29 ms. Haploid yeast cells in stationary phase are not capable of rejoining dsb. Using such cells proficient or deficient in the synthesis of glutathione (GSH), the lifetimes were found to be 0.37 or 0.49 ms for GSH-proficient (100 per cent GSH) and -deficient (2.1 per cent GSH) cells, which is in agreement with the view that chemical restitution of oxygen-dependent precursors is impaired in gsh- cells.

Cells, Cultured↗
PubMed1990

Distribution of cisplatin in tumor-free versus tumor-bearing B6D2F1 mice.

In healthy as well as in leukemia P388- or melanoma B16-bearing B6D2F1 mice the platinum concentrations in liver, serum and kidneys were determined after i.v. administration of 10 mg/kg cisplatin. In a tumor stage related to about 40% of the mean survival time (MST) no differences in platinum distribution between tumor-bearing and healthy animals could be observed. In the tumor stage related to about 70% of the MST, elevated platinum levels in serum of both tumor models and in kidneys only in melanoma-bearing but not in leukemia-bearing mice could be found. These results confirm those of other authors that tumor stages less than 50% of the MST exert no marked influence on the distribution pattern of cisplatin in rodents. Moreover, in advanced tumor stages distributional differences of antineoplastic agents may be expected between healthy and tumor-bearing mice as well as between animals bearing different neoplasias.

Animals↗
PubMed1988

Exponential or shouldered survival curves result from repair of DNA double-strand breaks depending on postirradiation conditions.

The yeast mutant rad54-3 is temperature conditional for the rejoining of DNA double-strand breaks, but cells do proliferate at both the restrictive and permissive temperatures. Thus, after irradiation with 30 MeV electrons, survival curves can be obtained which may or may not involve double-strand break rejoining under certain experimental conditions. Because of this special property of rad54-3 cells, it was possible to demonstrate that rejoining of radiation-induced double-strand breaks under nongrowth conditions yields exponential survival curves the slopes of which decrease as a function of the rejoining time. These survival data suggest that, under nongrowth conditions, the rejoining of double-strand breaks is an unsaturated process and lacks binary misrepair. In contrast, whenever rejoining of double-strand breaks occurs under growth conditions, shouldered survival curves are observed. This is true for immediate plating as well as for delayed plating survival curves. It is proposed that it is the unsaturated rejoining of double-strand breaks under nongrowth conditions, lacking binary misrepair, which is responsible for potentially lethal damage repair.

Cell Line↗
PubMed1987

Effect of cellular glutathione content on the induction of DNA double strand breaks by 25 MeV electrons.

The effect of endogenous glutathione (GSH) on the induction of DNA double strand breaks (dsb) by 25 MeV electrons was investigated using stationary haploid yeast cells defective in gamma-glutamyl-cysteine-synthetase (gsh 1) containing less than 5 per cent of the normal GSH content. In gsh 1 cells the induction of dsb is increased by a factor of 1.5 under oxic and 1.8 under anoxic irradiation conditions: whereas the oxygen enhancement ratio was only slightly decreased (1.9) compared to wild-type cells (2.4).

Cell Survival↗
PubMed1987

Potentially lethal damage repair is due to the difference of DNA double-strand break repair under immediate and delayed plating conditions.

Cells plated immediately after irradiation on nutrient agar (immediate plating) exhibit a lower survival than cells which are kept under nongrowth conditions before plating (delayed plating). The difference between the survival curves obtained after immediate plating and delayed plating is considered to exhibit the cell's capacity to repair potentially lethal damage. In yeast evidence has been presented previously for the DNA double-strand break (DSB) as the molecular lesion involved in the repair of potentially lethal damage observed at the cellular level. Radiation-induced DSB are repaired in cells plated on nutrient agar, i.e., under growth conditions, as well as in cells kept under nongrowth conditions. In this paper DSB repair under growth and nongrowth conditions is studied with the help of the yeast mutant rad54-3 which is temperature conditional for DSB repair. It is shown that the extent of repair of potentially lethal damage can be varied by shifting the relative fractions of repair of DSB under growth conditions versus nongrowth conditions. Repair of DSB in cells plated on nutrient agar is promoted when glucose is substituted by Na-succinate as an energy source. As a result the immediate plating survival curve approaches the delayed plating survival curve, thus reducing the operationally defined repair of potentially lethal damage. We show that this reduced potentially lethal damage repair is caused, however, by a higher amount of DSB repair in cells immediately plated on succinate agar as compared to glucose agar.

Cell Division↗
PubMed1986

Effectiveness of 1.5 keV aluminium K and 0.3 keV carbon K characteristic X-rays at inducing DNA double-strand breaks in yeast cells.

Induction of DNA double-strand breaks in diploid wild-type yeast cells, and inactivation of diploid mutant cells (rad54-3) unable to repair DNA double-strand breaks, were studied with aluminium K (1.5 keV) and carbon K (0.278 keV) characteristic X-rays. The induction of DNA double-strand breaks was found to increase linearly with absorbed dose for both characteristic X-rays. Carbon K X-rays were more effective than aluminium K X-rays. Relative to 60Co gamma-rays the r.b.e.-values for the induction of DNA double-strand breaks were found to be 3.8 and 2.2 for carbon K and aluminium K X-rays respectively. The survival curves of the rad54-3 mutant cells were exponential for both ultrasoft X-rays. For inactivation of rad54-3 mutant cells, the r.b.e.-values relative to 60Co gamma-rays were 2.6 and 2.4 for carbon K and aluminium K X-rays, respectively. The DNA double-strand break data obtained with aluminium K and carbon K X-rays are in agreement with the data obtained for gene mutation, chromosome aberrations and inactivation of mammalian cells, suggesting that DNA double-strand breaks are the possible molecular lesions leading to these effects.

DNA↗