[en] We examined the possibility that the polyamine was involved in the survival of cells against γ-irradiation in E. coli at low doses using polyamine-deficient mutant strain, KL527. In 40 Gy, 80 Gy and 200 Gy irradiated group, Survival of cells increased by 62%, 44% and 30% respectively by addition of polyamine putrescine (1 mM). When the dose of irradiation was 400 Gy, the survival of cells was 7% in the polyamine supplement condition and the survival colonies were not detected in the polyamine absent condition. Wild type strain MG1655 showed that the survivals of cells were 3.6% and 6.6% in both conditions at a dose of 400 Gy, respectively. (author)

[en] Electron paramagnetic resonance spectroscopy (EPR) of tooth enamel is a relatively new technique for retrospective dosimetry that in the past two years has seen increasing effort towards its development and evaluation. Efforts have centered on determining the accuracy which may be achieved with current measurement techniques as well as the minimum doses detectable. The study was focused on evaluating some factors which influence the accuracy of EPR dosimetry of enamel. Reported are studies on sample intercomparisions, instrumental considerations, and effects of dental x-rays, environmental sunlight and ultraviolet radiation

[en] Concentration versus radiosensitizing effect curves have been determined for four E.coli strains with two nitroaromatic sensitizers. The data are consistent with a simple competition kinetic model of sensitization, and K values for Ro 07-0582 are reported. An empirical relationship, DMF = αo.e.r., relating the dose-modifying factor produced by a given concentration of sensitizer to the oxygen-enhancement radio of a bacterium was found to hold for all the mutants tested for values of α>1/o.e.r. The limiting value of α at high concentrations of sensitizer was 0.75. Some implications of this relationship and the limiting value of α are discussed. (author)

[en] The effect of the continuous monochromatic coherent laser radiation on the survival rate of Saccharomyces cerevisiae of strain 14 is studied. The effect of laser radiation is judged by the change in the survival rate of the yeast culture before and after the irradiation. The decrease of the number of the yeast cells in the initial moments of the irradiation was observed as a result of the laser irradiation. Then the rapid decrease of the number of cells with time changes into their constant number. It is established that the low-energy coherent radiation decreases the survival rate by 30-40%

[en] The relative efficiencies by which chromosomal and extrachromosomal DNAs are repaired in irradiated bacteria were assayed. Repair-proficient Escherichia coli C600 cells lysogenic for, or infected with, the thermoinducible phage lambdacI857 ind were exposed to γ or uv radiation and then tested for colony- and plaque-forming ability. The results show that the bacterial cell is about 5 times more sensitive to γ rays and about 1.5 times more sensitive to uv light, if compared to either (1) the prophage that is irradiated in the bacterial chromosome and, on heat induction, repaired in the cytoplasm or (2) the infecting phage that is irradiated and repaired in the cytoplasm. Since the bacterial DNA is about 80 times larger than the phage DNA, it is inferred that repair processes operating along the chromosomal DNA are one order of magnitude more efficient than those operating along the extrachromosomal DNA. This conclusion is reinforced by the fact that the absence of repair in the system Escherichia coli AB2480 uvrA recA-lambdacI857 ind red gives the expected ratio of 80/1 for the uv sensitivity of cells and that of intracellular phage

[en] Mutagenic actions of ultraviolet irradiation (UV), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and acriflavine (photodynamic) were tested in free and intracellular phage AS-1 infecting Anacystis nidulans IU625. Spontaneous and induced mutations with particular reference to host range (h) and minute plaque formation (m) were investigated. The spontaneous mutation frequencies varied from 10^-9 to 10^-8 and from 2 X 10^-5 to 2 X 10^-4 for h and m mutants respectively. UV was efficient in inducing h and m markers in free phage particles as well as intracellular phage; MNNG induced both markers in intracellular phage only, and acriflavine induced m mutants only in free as well as in infecting phages. UV-induced mutations in free phage were photo-reactivable by visible light. With all the mutagens used, maximal induction of both markers was observed with treatment of 2-h complexes. (Auth.)

[en] Kinetics of the inactivation of phage T7 by six ultraviolet and visible light wavelengths of the far (below 320 nm) and the near uv (above 320 nm) were studied, with and without host-cell reactivation. Inactivations were always exponential with the three shorter wavelengths (254,313, and 334 nm), whereas with the longer wavelengths (365, 405, and 460 nm), a small shoulder (extrapolation number <2) was consistently obtained. The host-cell reactivation sector was prominent with 254 and 313 nm of radiation, reduced with 334 nm, and either trivial or absent with the three longer wavelengths. Action spectra for the inactivation revealed small shoulders in the near-uv region, both with and without host-cell reactivation. A comparison of single-strand break (alkali-labile bond) induction by 365 nm of radiation in phage T4, compared with lethality in phage T7, revealed that a frequency of 0.3 single-strand breaks may occur per lethal hit

[en] W-reactivation is reduced by recF143 and recF144 mutations and is undetectable if a second mutation at either the uvrA or uvrB locus is combined with recF143. The uvrA and uvrB mutations alone block W-reactivation partially. A recL152 mutation also partially blocks W-reactivation by itself. In combination with a uvrB5 mutation, recL125 blocks W-reactivation completely but in combination with recF143, significant residual W-reactivation ability remains. We suggest that the phenomenon of W-reactivation is the result of at least two modes or pathways. The observation that recF143 uvrB5 and recF143 uvrA6 strains permit normal levels of mutagenesis completely block all W-reactivation leads us to suggest further that the mechanism(s) of W-reactivation is at least partly different from that of UV mutagenesis. (orig.)

No abstract available

No abstract available