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P M Achey

Publications and source records attributed to P M Achey.

18 recordsLinked to original sources
PubMed1984

Excision repair participates in the Weigle reactivation of ultraviolet light-irradiated phi X174 double-stranded DNA.

The efficiency of Weigle reactivation of ultraviolet light-irradiated single and double-stranded phi X174 DNA by wild-type and excision repair-defective E. coli hosts was determined. After limited exposure to ultraviolet light, the efficiency of Weigle reactivation by an ultraviolet light-irradiated wild-type host was greater for double-stranded phi X174 DNA than for its single-stranded counterpart. However, the efficiency of inducible recovery of the double-stranded DNA molecule decreased as its exposure to ultraviolet light increased until it became constant at a value 1.5 times less than that for single-stranded form of phi X174 DNA. The efficiency of Weigle reactivation of the single-stranded DNA molecule by the same host, however, was independent of the dose to the DNA, as were the efficiencies of reactivation for both forms of phi X174 DNA by ultraviolet light-irradiated excision repair-deficient hosts. In excision repair-defective hosts the efficiency of Weigle reactivation of double-stranded phi X174 DNA was also 1.5 times less than that for the single-stranded molecule. These results suggest that the Weigle reactivation of double-stranded phi X174 DNA is mediated in part by an excision repair process, and that this component of Weigle reactivation eventually can be saturated by ultraviolet light-induced DNA damage leaving other repair processes, such as trans-damage synthesis, responsible for the remaining inducible reactivation.

Bacteriophage phi X 174↗
PubMed1983

Inducible repair of thymine ring saturation damage in phi X174 DNA.

The susceptibility to inducible SOS repair of 5,6-dihydroxy-dihydrothymine (t') damage in single-stranded phi X174 DNA has been measured. Following exposure to osmium tetroxide, which introduces t' damage in DNA under the conditions used, biological survival of the DNA infected into spheroplasts of Escherichia coli which had received prior exposure to ultraviolet light was higher than in unexposed spheroplasts. From our results, we conclude that approximately 63% of the biological damage from t' products, which is one of the classes of damage present in DNA following ionizing radiation, is susceptible to repair by the inducible SOS repair system.

Bacteriophage phi X 174↗
PubMed1981

Photoreactivating enzyme activity in the rat tapeworm, Hymenolepis diminuta.

There has been considerable speculation about the occurrence of photoreactivating enzyme in different organisms and about its biological purpose. We have developed a simple, sensitive assay for estimating pyrimidine dimers in DNA which is useful in making a rapid survey for the presence of the enzyme. Using this method, we have found photoreactivating enzyme activity in the tissues of the rat tapeworm Hymenolepis diminuta. This parasite spends the majority of its life span in the bodies of its definitive or intermediate hosts, but a period is spent externally. We suggest that photoreactivating enzyme may be important in preserving the integrity of embryonic DNA during this free-living stage.

Animals↗
PubMed1979

Photoreactivating enzyme in the blind cave fish, Anoptichthys jordani.

1. Exposure of cells to ultraviolet light induces molecular changes in DNA which may lead to cellular death. 2. One product, pyrimidine dimers, is reversed during subsequent exposure to visible light by photoreactivating enzyme. 3. Photoreactivating enzyme has been recorded in different organisms, but inconsistencies in its distribution suggest it may have other functions. 4. We have found photoreactivating enzyme in the blind cave dwelling fish, Anoptichthys jordani. 5. Sufficient time has elapsed in the cave environment to allow loss of features of importance to epigean fish, including the eyes and pigmentation. 6. The continued presence of the enzyme indicates that it may have other functions.

Adaptation, Physiological↗
PubMed1975

Induction of radioresistance in Escherichia coli.

The effect of prior treatment by inducing agents on the radioresistance of cells of Escherichia coli has been studied. In order to separate the induction process from the radiation-damage process, cells were first treated with inducing agents such as ultraviolet light, ionizing radiation, or nalidixic acid, allowed to become induced by incubation for 50 min and then given rifampin to prevent further induction. They were then tested for radiation sensitivity. It was found that all strains tested except recA-, lex-, and recB showed very apparent protection. Induction by UV had the most effect and by nalidixic acid the least. The time course of development of protection was observed in one case: it is 50% established in 15 min. The absence of effect in recA- and lex- is explainable by the fact that these cells cannot be induced, for example, for prophage or the inducible inhibitor of post-irradiation DNA degradation. We suggest that the inducible inhibitor of postirradiation DNA degradation is one factor in a recovery system possessed by E. coli cells.

Cell Division↗
PubMed1973

Equal sensitivity of the two strands of phiX174 replicative DNA to breakage by ionizing radiation.

The supertwisted, double-stranded, replicative intermediate of øX174 DNA (RFI) has been used to determine whether one of the two strands of the double helix is uniquely sensitive to induction of single-strand breaks by ionizing radiation. This could result from a particularly sensitive base sequence or a transfer of energy to a specific location of the DNA molecule. The results indicate that both strands of the double helix are equally broken, even though their base compositions are significantly different. If there are "hot spots" in the strands, then they are present in equal amounts in each strand.

Carbon Isotopes↗
PubMed1967

Deoxyribonucleic acid repair replication after ultraviolet light or x-ray exposure of bacteria.

A comparison of repair synthesis after ultraviolet light (UV) or X-ray exposure was made in Escherichia coli strains 15T(-) (555-7) and B/r by use of a D, (15)N, (13)C density labeling system. During the initial 15 min of incubation after UV irradiation, both a "repair" synthesis and a reduced semiconservative deoxyribonucleic acid (DNA) synthesis occurred. In the so-called "physiological" dose range used, the latter was greater than the former. X-irradiation of cells, at doses producing similar levels of cell death as in the UV-exposed cultures, did not lead to a similar repair replication process. However, a density heterogeneity of the DNA synthesized in the initial 10 min after exposure was observed. This is interpreted in terms of X ray-induced DNA degradation. Normal cells showed only a semiconservative type of replication and, therefore, within the limits of resolution of the system used (the incorporation of 1,000 to 5,000 nucleotides per replicating chromosome could be measured), DNA in normal cells did not appear to undergo a repair synthesis involving thymine exchange. These results indicate that not all repair mechanisms mimic that found after UV exposure.

Ammonium Chloride↗