The tumor suppressor p53 enhances repair of UVC-induced DNA damage. The comet-nuclear extract (comet-NE) assay, a conventional alkaline comet assay which includes a nuclear digestion step, was used to examine the effects of p53 on the excision activity of nuclear extracts (NEs). In contrast with untreated NEs, NEs immunodepleted of p53 or NEs of p53-null cells were unable to excise UVC-induced DNA adducts. Introduction of p53 by transfection restored the excision activity to NEs of p53-null cells. Deletion of the N-terminal 99 amino acids and/or the C-terminal 75 amino acids of p53 barely affected the excision activity, whereas further deletion of the C-terminus of p53 by another 20 amino acids completely abolished the excision activity of NEs. Immunostaining following localized UV irradiation was used to examine the effects of p53 on the recruitment of repair proteins for nucleotide excision repair (NER). Although recruitment of XPC occurred regardless of the presence of p53, the recruitment of XPB was p53-dependent. However, p53 with the 95 amino acid deletion at its C-terminus was unable to support this recruitment of XPB. Consistently, intact p53 or C-terminal 75 residus truncated version (but not the C-terminal 95 residue truncated version) was detected in co-immunoprecipitation assays with an anti-XPB antibody. These results support the hypothesis that p53 facilitates NER through direct involvement by protein-protein interactions.

抑癌基因P53可以促進細胞修補紫外線所造成的DNA損傷。在本實驗中利用彗星-核萃取物分析法(藉由鹼性彗星分析法引進核萃取物切割的動作)來測試P53對於核萃取物切割能力之影響。相對於未做任何處理之核萃取物，利用免疫耗竭方式由核萃取物中移除P53或是不含P53的細胞核取萃物無法去切割紫外線造成之DNA損傷。利用P53穩定性轉染之不含P53細胞的核萃取物可以回復其切割的活性。切除P53 N端99個及C端75個胺基酸不會影響其切割之活性，然而再多切除C端20個胺基酸則會完全抑制其切割之活性。利用局部紫外線照射後進行免疫染色的方法來研究P53如何影響核酸切除修復中修補蛋白質聚集之情形。雖然XPC之聚集與P53的存在與否無關，但XPB則與P53有關。當切除P53 C端95個胺基酸則XPB無法聚集。同樣的,利用共免疫沈澱方法發現只有完整的P53或是切除P53 C端75個胺基酸會和XPB一起被抗體抓下來，而P53 C端切除95個胺基酸的則不會。這些結果支持我們的假設，P53是藉由蛋白質之間的交互作用直接來促進核酸切除修復。

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