海藻糖（trehalose）是由兩個葡萄糖分子藉α,α-1,1-鍵結而成的非還原性雙糖，自然界中即存在，常見於植物、低等無脊椎動物以及大多微生物如真菌、細菌及古生菌中。海藻糖在自然界所扮演的角色是生物體抵抗逆境的重要分子。被認為是穩定蛋白質、細胞膜與DNA，提高存活率的重要因素。細胞內的海藻糖是否能夠提供DNA對放射線的保護性，目前尚未見報導。本研究在證明E. coli細胞內的海藻糖能提供DNA對UV破壞的保護效果。藉由對pyrimidine dimer具專一性的T4 pdg酵素切割，以及DNA鹼性電泳的定量分析，決定不同UV照射劑量下DNA所產生的cyclobutane pyrimidine dimers （CPDs），以此為判斷DNA損傷程度的主要指標。並分析DNA傷害程度與海藻糖之間的關係。首先在活體外，以萃取純化好的E. coli基因體DNA混合在不同濃度的海藻糖中進行UV照射，確認了UV劑量越高，對應DNA完整性越低，而且在相同劑量下，高濃度海藻糖（100 mM）對DNA的保護效果較低濃度或不含海藻糖要好。在活體E. coli細胞內，藉由誘導海藻糖合成酶基因的表現使細胞內累積海藻糖，並進行UV照射加以分析，結果發現累積海藻糖的菌株在720 J/m2 的UV劑量下所造成的傷害為22 CPDs/Mbs，沒有累積海藻糖的菌株則是46 CPDs/Mbs。此研究結果證明海藻糖不但在活體外提供DNA抵抗UV之保護性，同時在證明在活體細胞中的海藻糖也具有保護DNA抵抗UV對其結構的破壞作用。

Trehalose, a non-reducing disaccharide compound, consists of two glucose by the α,α-1,1- glycosyl bond. It exists naturally in plants, invertebrates, fungi and most prokaryotes, like bacteria. Some reports suggest that trehalose is important for organisms to resist the stress, and it also plays an important role to make protein, membrane and DNA molecules more stable. However, there is no report suggests the protection by trehalose of DNA from UV irradiation in vivo. Our objective is to confirm the protection of DNA by trehalose from UV in vivo. We quantify the formation of cyclobutane pyrimidine dimers (CPDs) in DNA under multiple dosage of UV irradiation by alkaline gel electrophoresis with pyrimidine dimer specific T4 pdg digestion. Formation of CPDs is an important index to determine the level of DNA damage, and we analyze the relationship between DNA damage and trehalose. First, we extract genomic DNA from E .coli and mix with multiple dosage of trehalose, then make the mixture expose to UV light. We found the levels of intact DNA decreased with increasing UV dosage, and the DNA mixed with 100 mM trehalose showed more intact than that mixed with less trehalose. We make E. coli accumulate intracellular trehalose in vivo by induction of trehalose synthase, and then exposed to UV irradiation, followed by analysis. The results show that the cells with accumulated trehalose formed 22 CPDs/Mbs under UV dosage of 720 J/m2, and cells without intracellular trehalose formed 46 CPDs/Mbs. According to these results, trehalose not only protect DNA from UV in vitro, but also perform protection of DNA against structure damage from UV irradiation in vivo.

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