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D Frankenberg

Publications and source records attributed to D Frankenberg.

52 records · Page 3Linked to original sources
PubMed1984

Split-dose recovery is due to the repair of DNA double-strand breaks.

DNA double-strand breaks are the molecular lesions the repair of which leads to the reappearance of the shoulder observed in split-dose experiments. This conclusion is based on results obtained with the help of a diploid yeast mutant rad 54-3 which is temperature-conditional for the repair of DNA double-strand breaks. Two repair steps must be met to yield the reappearance of the shoulder on a split-dose survival curve: the repair of double-strand breaks during the interval between two doses and on the nutrient agar plate after the second dose. In yeast lethality may be attributable to either an unrepaired double-strand break (i.e. a double-strand break is a potentially lethal lesion) or to the interaction of two double-strand breaks (misrepair of double-strand breaks). Evidence is presented that the two cellular phenomena of liquid holding recovery (repair of potentially lethal damage) and of split-dose recovery (repair of sublethal damage) are based on the repair of the same molecular lesion, the DNA double-strand break.

Cell Line↗
PubMed1984

Interpretation of the dose and LET dependence of RBE values for lethal lesions in yeast cells.

Survival data on yeast cells proficient or deficient in the repair of DNA double-strand breaks (dsb) and data on the induction of dsb are used to interpret the dose dependence of the RBE value for lethal lesions after irradiation at high dose rate followed by 72-hr liquid holding providing optimum conditions for repair of potentially lethal lesions (RBEDP, DP = delayed plating). The radiations applied are conventional (150 kV), soft (50 kV), and ultrasoft (4 kV) X rays, 30-MeV electrons (or 60Co gamma rays), and 3.5-MeV alpha particles. Analysis shows that the dose dependence of the RBEDP value can be explained by the combination of two dose-independent RBE values, one for the single-particle traversal effect (RBEspt) and the other for the accumulation of dsb (RBEdsb) due to the traversal of more than one particle through the cell nucleus. Furthermore, it is shown that the LET dependence of RBEspt values describing the linear component of the lethal lesions must be considered separately for "electron" and "particle" radiations.

Alpha Particles↗
PubMed1984

Repair of DNA double-strand breaks as a determinant of RBE of alpha particles.

The role of repair of DNA double-strand breaks (dsb) in the determination of the RBE-value of alpha particles was studied using the temperature conditional radiosensitive diploid yeast mutant rad 54-3. This mutant is proficient in the repair of dsb at the permissive temperature of 23 degrees C at which it yields a shouldered survival curve, but it is dsb repair-deficient at the restrictive temperature of 36 degrees C at which it yields an exponential survival curve. At the permissive temperature the rad 54-3 mutant also shows liquid holding recovery of colony forming ability as a function of the liquid holding period. Thus, with this mutant it is possible to obtain survival curves involving no repair of dsb (immediate plating, 36 degrees C), partial repair of dsb (immediate plating, 23 degrees C) and gradually increasing levels of dsb repair by delayed plating after liquid holding periods of 24, 48 and 72 h. The RBE-values of densely ionizing 3.5 MeV alpha particles for cell killing relative to sparsely ionizing 30 MeV electrons have been determined as a function of the level of dsb repair. It is shown that the RBE-value is low and independent of dose when no repair of dsb is involved, whereas it becomes gradually larger with a gradual increase in the level of dsb repair.

Alpha Particles↗
PubMed1984

Interpretation of the shape of survival curves in terms of induction and repair/misrepair of DNA double-strand breaks.

Evidence is presented that in yeast cells one DNA double-strand break (dsb) may be considered as one potentially lethal lesion (PLL). Using a temperature conditional radiosensitive diploid yeast mutant (rad 54-3) it is demonstrated that the shoulder of survival curves, for cells plated immediately, is due to repair of dsb (PLL) within a restricted time period. Split dose experiments with the mutant rad 54-3 show that the reappearance of a shoulder is observed when two conditions are met: (1) repair of dsb (PLL) during the time interval between doses and (2) repair of mainly those dsb (PLL) which are induced by the second dose on the nutrient agar plate. Irradiation of wild type yeast cells at high dose rate followed by liquid holding treatment for 72 h (delayed plating, DP) or at low dose rate show that the bending of DP-survival curves is due to the accumulation of dsb (PLL) leading to lethal lesions probably by misrepair of dsb.

DNA↗
PubMed1979

The influence of oxygen on the survival and yield of DNA double-strand breaks in irradiated yeast cells.

Survival and induction of DNA double-strand breaks were studied in cells of Saccharomyces cerevisiae irradiated under oxic or anoxic conditions with 30 MeV electrons. A linear relationship between DNA double-strand breakage and dose was found in both cases. The o.e.r.-value for colony forming ability was found to be 1.9 +/- 0.2, whereas the o.e.r.-value for DNA double-strand breakage was 3.0 +/- 0.1. These results are not inconsistent with the idea that DNA double-strand breaks are involved in killing of yeast cells. The frequency of induction of DNA double-strand breaks was found to be 0.74 x 10(-11) double-strand breaks per g/mol per Gy when cells were irradiated under oxygen and 0.24 x 10(-11) double-strand breaks per g/mol per Gy under nitrogen.

Cell Survival↗
PubMed1979

Reparable and irreparable damage in yeast cells induced by sparsely ionizing radiation.

It is shown that in diploid yeast there are significant differences in the extent of irreparable damage after irradiation with X-rays, 60Co-gamma-rays and 30 MeV electrons. At extremely low dose rates, 60Co-gamma-rays were found to produce almost no irreparable damage at least up to 1200 Gy. X-rays, however, at the same low dose rate caused irreparable damage in the same dose range yielding a surviving fraction of 0.25 at 1200 Gy. For irradiations at high dose rate followed by liquid holding recovery the relative biological effectiveness of X-rays amounted to at least 4 for absorbed doses of up to 1000 Gy. With 30 MeV electrons at high dose rates an accumulation of sublethal and potentially lethal damage resulting in irreparable damage occurred above 1000 Gy. It is suggested that irreparable damage in yeast is due to a cooperative effect of neighbouring track ends.

DNA Repair↗