| Budget Amount *help |
¥3,800,000 (Direct Cost: ¥3,800,000)
Fiscal Year 2004: ¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 2003: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Research Abstract |
Reactive oxygen species (ROS) generated by irradiation and by respiration as byproducts are well-known as risk factors for aging and cancer. ROS oxidze DNA. Consequently accumulation of the modified DNA bases could occur by being escaped from DNA repair and it could lead to genetic mutations. A major DNA repair system against the oxidative DNA is base excision repair (BER) which is initiated by DNA glycosylase, although it is unclear as to how much DNA glycosylase contributes to abrogate the aging and carcinogenesis because knock-out mice deficient of the known glycosylase, OGG1 or NTH1, do not show such phenotypes.
We have discovered novel mammalian DNA glycosylases, NEIL1 and NEIL2, which are similar to bacterial Nei, Fpg glycosylases, and substrate specificity of NEIL1 overlaps NTH1. Furthermore, we have biochemically characterized DNA glycosylases, TGG1 and TGG2 showing excision activity of thymine glycol (a major oxidative thymine). Identification of the gene for TGG1 and TGG2 was unsuccessful although we demonstrated that they are different species from known DNA glycosylases such as NEIL1 or NTH1. On the other hand, we cloned and characterized third Nei-like glycosylase, NEIL3, from human. NEIL3 shows AP-lyase activity as is the case of Fpg, Nei glycosylase family. The activity is highly specific for single-stranded DNA. NEIL3 also act as DNA glycosylase for certain oxidative bases created by in vitro DNA oxidation treatment. NEIL3 expression is tissue specific (highest in thymus, spleen and testis). Evidence of the oxidative DNA repair function of NEIL3 was also obtained. Correctively, we propose that overlapping function of a variety of DNA glycosylases for mammalian BER, and that there may be an uncharacterized repair pathway of BER from the fact of the single-stranded specific activity of NEIL3.
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