Abstract
In mammalian cells, nucleotide excision repair (NER) is the main mechanism to repair DNA damage induced by UV irradiation. Previously, p53 has been shown to be indispensible in excision activity of nuclear extract by using comet-nuclear extract (comet-NE) assay. The essential sequence of p53 in the regard has been mapped to amino acid residues 299-308. This study is focused on the effect of deletion of amino acid residues 299-308 p53 on repair of UV-induced DNA damage. In situ study with cells expressing deletion 299-308 p53 shows the reduction of both NE incision activity and the ability of resolving DNA double helix at DNA damage sites. The experiments with synthesized peptides further confirm the importance of this sequence in p53:XPB interaction. When the p53 299-308 a.a. sequence-derived peptides were incubated with the nuclear extract prior to the comet-NE assay, the excision activity of NE was abolished as expected. We further proved that this synthetic peptide is able to interact with XPB, and to diminish the p53:XPB interaction. Moreover, in comparison to the wild type sequence, the peptide with alanine substitutions at both Lys 305 and Arg 306 completely lost the inhibitory effect, showing the electrostatic nature between p53 and XPB. Thus, the results provide evidence that the peptide derived from the sequence of interest may be used for drug screening.

中 文 摘 要
核苷酸切除修復是哺乳類細胞用以修復紫外光造成去氧核醣核酸傷害的主要機制。先前研究藉由彗星-細胞核萃取物的實驗指出，抑癌因子p53在核苷酸切除修復中扮演不可或缺的角色，並且將參與核苷酸切除修復的p53氨基酸序列鎖定在第299到308個胺基酸。這篇論文關注於p53胺基酸序列299-308透過XPB蛋白質參與核苷酸切除修復的影響。論文中的實驗結果顯示缺少胺基酸序列299-308的p53蛋白質會減低細胞核萃取物解開去氧核醣核酸雙股螺旋以及切除去氧核醣核酸上的共價連結物的能力。另外在細胞核萃取物中，合成的p53 299-308胺基酸序列胜肽會與正常的p53蛋白質競爭與XPB蛋白質的結合，並且消除核苷酸切除修復中切除共價連結物的能力，更加證實p53 299-308胺基酸序列在與XPB蛋白質結合影響核苷酸切除修復的重要性。除此之外，論文中利用丙胺酸取代p53 299-308胺基酸序列胜肽中的賴氨酸與精氨酸消除了p53 299-308胺基酸序列胜肽對核苷酸切除修復的抑制，提供了p53和XPB蛋白質間可能藉由帶電性的胺基酸結合的可能性。本篇論文提供了關於p53 299-308胺基酸序列藉由與XPB蛋白質交互作用，進而影響核苷酸切除修復機制的實驗數據，而合成的p53 299-308胺基酸序列胜肽也提供了篩選p53抑制藥物的途徑。

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