1. Outlines and History
Deinococcus radiodurans (figure 1) is a non-pathogenic bacterium that habitats various earth's environment. The most striking feature of D. radiodurans is its extremely radioresistance phenotype. They show the most resistance to ionizing radiation among all the living organisms: 100-fold and more than 1,000-fold resistant compared to Escherichia coli and human cell, respectively. Previous studies revealed that D. radiodurans possesses high capacity for repairing ionizing radiation-induced DNA damage. However, the mechanisms underlying its radioresistance had yet to be determined. In 1999, The Institute for Genomic Research, USA, determined the genome sequence of D. radiodurans. The genome analysis, however, could not clarify the radioresistance mechanisms.

JAEA investigated D. radiodurans using gamma irradiation facility and ion beam irradiation facility (TIARA) located in Takasaki Advanced Radiation Research Institute in order to clarify what gene is important in radioresistance. In consequence, we found out a gene named pprA and applied for a patent in 2001. Protein PprA derived from the pprA gene had no similarity to any other hitherto known proteins. Subsequent biochemical studies revealed that PprA protein preferentially bound to ionizing radiation-induced DNA strand breaks, and thereby stimulated DNA repair (Figure 2).

2. Achievement of the practical use
The repair of DNA strand breaks is used in fundamental genetic engineering technique such as DNA cloning. Therefore, we considered that PprA protein could be useful as a new biotech reagent. Nippon Gene Co., Ltd., Toyama, who licensed from JAEA, released a new DNA repair reagent “TA-Blunt Ligation Kit” (figure 3) which used the PprA technology, November 18, 2005. Prior to the achievement of the practical use, JAEA advanced a proposal on the practical application of the PprA technology, actively engaged in providing samples and giving technical guidance to Nippon Gene through the technology transfer support program of Japan Science and Technology Agency.
Hereafter, broad-ranging utilization of the DNA repair kit is expected in genetic engineering field including genetic diagnosis and the development of new medications.