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Success in Selective Induction of DNA Damage by Synchrotron Radiation Soft X-Rays - Hopes for its application to new DNA manipulation technology (Press Release)

Release Date
05 Nov, 2009
  • BL23SU (JAEA Actinide Science)
A research team led by Kentaro Fujii, Research Scientist of the Basic Radiation Research Group at the Advanced Science Research Center, Japan Atomic Energy Agency, has succeeded in selectively inducing DNA damage using soft X-rays at SPring-8 for the first time in the world.

Japan Atomic Energy Agency

A research team led by Kentaro Fujii, Research Scientist of the Basic Radiation Research Group at the Advanced Science Research Center, Japan Atomic Energy Agency (JAEA; Toshio Okazaki, President), has succeeded in selectively inducing DNA damage2) using soft X-rays1) at SPring-8 for the first time in the world. We hope that this technique will be applied to new DNA manipulation technologies in medical research related to DNA repair and in the development of industrial applications of DNA nanodevices.

JAEA has so far studied how to induce DNA damage, which is considered as a leading cause of cell death and mutation after irradiation, using the soft X-rays produced at SPring-8. We can selectively control the energy of soft X-rays using a monochromator, enabling the high-efficiency ionization3) of a certain element in DNA, which was difficult to achieve by conventional radiation. Carbon, nitrogen, and oxygen atoms in DNA were selectively ionized by selecting the appropriate energy of soft X-rays, and the frequency of various types of DNA damage induced by ionization was investigated. By the selective ionization of different elements, they succeeded in inducing the following three types of DNA damage at different efficiencies: DNA strand breaks4) and the mutations of nucleotide bases5) (purine and pyrimidine bases), which are two of the building blocks of nucleic acids that carry genetic information.

This research provided basic findings concerning the induction process of DNA damage, which are expected to be of importance in fields related to the risk assessment of radiation for living organisms and to radiation medicine. Part of this research was supported by Grants-in-Aid for Young Scientists (B) and Scientific Research (B). The achievements were published in the American chemistry journal, Journal of Physical Chemistry B, in the middle of November 2009.

Publication:
"Nucleobase Lesions and Strand Breaks in Dry DNA Thin Film Selectively Induced by Monochromatic Soft X-rays"
Kentaro Fujii, Naoya Shikazono and Akinari Yokoya
Journal of Physical Chemistry B, 113 (49), pp 16007–16015 (2009), Published online November 12, 2009.

<Figure>

Fig. 1 Soft X-ray beamline and vacuum chamber for irradiation of DNA sample installed at beamline

Fig. 1 Soft X-ray beamline and vacuum chamber for
irradiation of DNA sample installed at beamline

Fig. 2 Various types of DNA damage

Fig. 2 Various types of DNA damage

Fig. 3 Detection of plasmid DNA strand breaks by gel electrophoresis

Fig. 3 Detection of plasmid DNA strand breaks by gel electrophoresis
(When the dose of soft X-ray irradiation increases, the number of closed circular
DNA molecules that were present before irradiation decreases and the number of
open circular DNA molecules that are generated by irradiation increases.)

Fig. 4 DNA strand breaks due to mutation of nucleotide bases induced by Fpg and Nth proteins

Fig. 4 DNA strand breaks due to mutation of nucleotide
bases induced by Fpg and Nth proteins

Fig. 5 Dependence of frequency of inducing each type of damage on photon energy

Fig. 5 Dependence of frequency of inducing each type of damage on photon energy
(blue square, DNA strand breaks; red circle, mutation of purine bases; green trigona, mutation of pyrimidine bases).
(Energies required for ionization of carbon, nitrogen, and oxygen atoms are shown by
dotted lines in the figure. Each element absorbs light at these or higher energies (indicated by arrows)).

Fig. 6 Schematic of selective induction of DNA damage

Fig. 6 Schematic of selective induction of DNA damage

<Glossary>

1) Soft X-rays
Soft X-rays are X-rays with a low energy of approximately 0.1 - 2 keV and a low penetration ability.

2) DNA damage
DNA damage involves an irreversible change in the molecular structure of DNA. DNA damage can be roughly classified into the mutation of nucleotide bases, DNA strand breaks, and DNA crosslinks.

3) Ionization
Ionization is the physical phenomenon by which electrically neutral substances are converted to positively or negatively charged atoms or atomic groups. It is also called electrolytic dissociation. When an electron is emitted from a molecule upon ionization, a positive hole (a hole resulting from the shortage of electrons that appears to be positively charged) is generated in the molecule.

4) DNA strand breaks
The frame of a main chain of deoxyribose sugar and phosphate in one of the helical double DNA strands is broken. DNA strand breaks are caused by the damage due to the hydrolysis of sugar sites etc.

5) Nucleotide bases
DNA is a nucleic acid that carry genetic information and is composed of four nucleotide bases, namely, purine bases (adenine and guanine) and pyrimidine bases (thymine and cytosine). In the DNA double helix, adenine and thymine form a base pair via hydrogen bonding, as do guanine and cytosine.

Nucleotide bases

For more information, please contact:
Dr. Kentaro Fujii (Japan Atomic Energy Agency)
e-mail:mail.