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Shikazono, Naoya; Pearson, C.*; Thacker, J.*; O'Neill, P.*
no journal, ,
no abstracts in English
Sghaier, H.; Oba, Hirofumi; Sato, Katsuya; Mitomo, Hiroshi*; Narumi, Issei
no journal, ,
The order in which DNA of radiation-resistant prokaryotes has been subjected to constant damage through radiation, elevated temperature, dry, or reactive oxygen species during Earth evolution is important to investigate for a better understanding of environment-genome evolutionary relationship. In analyzing model genomes of radioresistant prokaryotes (
and 
), this study assesses the evolutionary itinerary of rough-and-tumble route on which their DNA was assaulted. Together with the examined literature, our analyses suggest the following elements. (1) Based on statistics of ORFs (Open Reading Frames) similarity relationships, we support the hypothesis that radiation resistance is a unique molecular reflection of the early Earth resilience and desiccation tolerance is a mark of cells that colonized land during the Archaean epoch. (2) Using unconventional methods, including oligonucleotide frequencies, numerous compelling data evoke the hypothesis that and progenitor(s) adapted, at least once, to the same environmental pressure, most probably ionizing radiation, through the acquisition of foreign genetic elements from one abnegator or compositionally similar abnegators. In conclusion, we present a model that satisfactorily accounts, from evolutionary perspectives, for DNA damage in radiation-resistant prokaryotes.
-raysAkamatsu, Ken
no journal, ,
Low-energy electrons emitted from DNA constituent atoms after irradiation with ultrasoft X-rays (USX) have been suggested to tend to form severe DNA damage. The aim of this study is to clarify the difference of DNA damage such as a cleavage pattern directly induced by USX from that by Co-60 -rays. USX- irradiation was performed using a beamline BL23SU at SPring-8. To characterize the cleavage sites, digestion velocity of the irradiated DNA pretreated with or without calf intestinal alkaline phosphatase by snake venom phosphodiesterase (SVPD) was measured. SVPD is an exonuclease producing a deoxynucleoside-5'-monophosphate one after another from a 3'OH terminal. The alkaline phosphatase treatment enables some of the SVPD-resistant sites to be digestive by SVPD. The initial digestion velocity is expected to give us information about the cleavage sites such as the amount, the chemical structure and the degree of overhang at the dsb sites. In this presentation, we will discuss variations of DNA cleavage produced by ionizing radiations, suggested by the experiments based on enzyme reaction kinetics.
Yokoya, Akinari
no journal, ,
One of the goals of our study is to clarify the nature of DNA damage in relation to the energy deposition pattern of radiation. The yields of single- and double-strand breaks, base lesions and clustered damage induced in closed-circular plasmid DNA (pUC18) were measured after exposing to various kinds of radiation (ion particles; 20 to 500 keV/
m, photons; 0.4 keV to 1.3 MeV). To focus on the effect of direct energy deposition from radiation track, we chose dried and hydrated DNA (35 water molecules per nucleotide). Base excision repair enzymes were used to detect the oxidative base lesions. In order to obtain more detailed insights into the physicochemical mechanism of DNA damage induction, short-lived base radicals and desorbed ion fragments from DNA related compounds were also measured by applying an EPR and ion-mass spectrometer at a synchrotron ultrasoft X-ray beamline. In addition, E. coli cells were used as a biological probe to study the nature of radiation-induced DNA damage. Experimental evidence obtained by these methods will be discussed in comparison with the plasmid data.
Wada, Seiichi*; Funayama, Tomoo; Matsumoto, Yoshihisa*; Oto, Takayo*; Sakashita, Tetsuya; Hamada, Nobuyuki*; Kakizaki, Takehiko; Hosoi, Yoshio*; Suzuki, Norio*; Kobayashi, Yasuhiko
no journal, ,
no abstracts in English