Quinoid radiotoxins in the blood of gamma-irradiated dogs

Quinoid radiotoxins were found in the peripheral blood 3-4 h following gamma-irradiation of dogs with doses of 5.76 Gy. The authors developed a simple method of isolation and purification of quinoid radiotoxins and specified their physicochemical and biological characteristics.     

Undulating kinetics factors in radiation mutagenesis]

Air-dry Crepis capillaris seeds, soaked for 14 and 20 hours, were dried to the moisture content of 1,1% with the following gamma-irradiation at a dose of 1500 r. Irradiated seeds were stored in the state of identical moisture for 38 days. The drying of three groups of seeds to moisture content of 1,1% provided their identical initial radiosensitivity. In the course of the storage mutability of treated seeds significantly increased as compared with the yield of mutations in non-stored seeds, and revealed undulating kinetics that involved all types of arising chromosome and chromatid rearrangements. The character of undulating kinetics is due to a correlation between functional state of nucleus (early G1, late G1, S) and water content in seeds.     

Base substitution mutagenesis by terminal transferase: its role in somatic mutagenesis

We have addressed the possibility of terminal transferase involvement in somatic mutagenesis and the creation of N-region diversity, by measuring the ability of TdT to enhance single-base substitution mutagenesis during in vitro DNA synthesis. Using 3 independent assays we find that terminal transferase produces only a small increase in base-substitution mutagenesis when assayed in the presence of DNA polymerase-β. In the presence of either polymerase- or E. coli polymerase-I, however, no detectable increase in TdT-induced mutagenesis is seen. Furthermore, in an assay capable of detecting a variety of mutational events, terminal transferase primarily produces complex addition/deletion mutations, as well as a few multiple, tightly-clustered, single-base mutations. We conclude that the majority of the scattered single-base changes that occur during antibody gene differentiation are not catalyzed by terminal transferase, but instead result from another error-prone DNA synthetic process (possibly utilizing DNA polymerase-β).     

Dual role of NER in mutagenesis in Pseudomonas putida

Nucleotide excision repair (NER) is one of the most important repair systems which counteracts different forms of DNA damage either induced by various chemicals or irradiation. At the same time, less is known about the functions of NER in repair of DNA that is not exposed to exogenous DNA-damaging agents. We have investigated the role of NER in mutagenesis in Pseudomonas putida. The genome of this organism contains two uvrA genes, uvrA and uvrA2. Genetic studies on the effects of uvrA, uvrA2, uvrB and UvrC in mutagenic processes revealed that all of these genes are responsible for the repair of UV-induced DNA damage in P. putida. However, uvrA plays more important role in this process than uvrA2 since the deletion of uvrA2 gene had an effect on the UV-tolerance of bacteria only in the case when uvrA was also inactivated. Interestingly, the lack of functional uvrB, uvrC or uvrA2 gene reduced the frequency of stationary-phase mutations. The contribution of uvrA2, uvrB and uvrC to the mutagenesis appeared to be most significant in the case of 1-bp deletions whose emergence is dependent on error-prone DNA polymerase Pol IV. These data imply that NER has a dual role in mutagenesis in P. putida-besides functioning in repair of damaged DNA, NER is also important in generation of mutations. We hypothesize that NER enzymes may initiate gratuitous DNA repair and the following DNA repair synthesis might be mutagenic.     

Exposure of human lymphocytes to ionizing radiation reduces mutagenesis by subsequent ionizing radiation

The effect of prior incubation with [3H]thymidine on survival and mutagenesis after X-irradiation of human lymphocytes was studied by incubating lymphocytes with 0.001-1.0 mu Ci/ml [3H]thymidine for 6 h at 37 degrees C and then irradiating with 150 or 300 rad. Survival was measured using lymphocyte cloning and mutagenesis was measured using 6-thioguanine selection to detect clones mutated at the hypoxanthine phosphoribosyltransferase locus. [3H]Thymidine alone had no effect on survival or mutagenesis and X-radiation alone produced the expected decrease in survival and increase in mutations. [3H]Thymidine prior to X-radiation had no effect on lethality of X-radiation but at concentrations of 0.1 and 1.0 mu Ci/ml produced a significant decrease in the number of mutations induced after both 150 and 300 rad. The results suggest that ionizing radiation, produced by disintegration of 3H, reduces the mutagenic effect of a subsequent exposure to ionizing radiation by induction of a system which prevents or repairs a restricted class of radiation damage.     

Study of the mechanism of mutagenesis directed by phosphotriester analogs of oligonucleotides. The role of repair in mutagenesis

The mutation system has been suggested in an effort to test insertion and deletion mutants by changing the Lac-phenotype of bacterial colonies transformed by mutant DNA. This system also makes possible to determine heterozygotes and homozygotes among the mutants. The yield of mutants in shown to depend on the structure of the DNA heteroduplex region. The yield of deletion mutants is greater than that of insertion mutants. Heterozygotes prevail in mutant colonies (greater than 90%).