1996 Fiscal Year Final Research Report Summary
A new aspect in DNA damages induced by sunlight-possible involvement of damages on guanine and 5-methylcytosine
| Project/Area Number |
07839010
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 時限 |
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| Research Field |
光生物学
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| Research Institution | Okayama University |
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Principal Investigator |
NEGISHI Kazuo Okayama Univrsity, Gene Research Center, Associate Professor, 遺伝子実験施設, 助教授 (70116490)
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| Project Period (FY) |
1995 – 1996
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| Keywords | Phage M13mp2 / Mutagenesis / %-methylcytosine / UV light / Sunlight / 8-oxoguanine / Skin cancer / mutM |
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| Research Abstract |
It is well known that sunlight is both carcinogenic and mutagenic. However, nature of the DNA damages causing mutation and cancer have yet well understood. Here we tried to analyzed DNA damages induced by sunlight mainly using sunlight itsel f as a UV source. In this project we focused on the damages of guanine and 5-methylcytosine.
Previously we found that sunlight induced G-to-C transition in phage M13mp2. This mutagenic specificity indicates the formation of guanine damages by sunlight exposure on the phage. In constrast, UVB irradiation caused mutations at pyrimidines. Therefore, we postulate that DNA damaging effects of sunlight is different from those of UVB.Next we analyzed the mutM sensitivity of the possible guanine damages caused by sunlight exposure. There was found no difference in the mutability of M13mp2 between in the assays on mutM^+ host and mutM^- host. This results indicated that the mutagenic leison were not able to be repaired by mutM system.
We also studied photoreaction on 5-methylcytosine. This base has much greater absorption coefficient at wavelengths over 300 nm. The UV light around 300 nm is believed to be most important for the genotoxic effects of sunlight. However its photodegaradabilty has not been compared extensively with cytosine and thymidine. As model compounds, photoreaction of 5-methyldeoxycytidine (mC) and dCpdmC were studied. Upon irradiation by germicidal lamp peaking at 254 nm, deoxycytidine seemed to be converted to deoxycytidine hydrate as reported in the literature. 5-methyldeoxycytidine also degraded at a slower rate than deoxycytidine. Next reactivities of, a dinucleoside monophosphate, was analyzed. Two major peaks among the products from dCpdmC seemed to be 6-4 photoproduct and its dewar isomer.
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