古氏-蛋白質是早先發現於自體免疫缺失病人血清中的一種自體抗原。結構含一個質量為70千道頓與一個質量為80千道頓的蛋白質單元次體，以非共價鍵結合而組成異型雙次體。古氏-蛋白質以此種異型雙次體的型態，與去氧核苷酸的末端、斷裂處或是單股轉換到雙股之過度型等結合，並在去氧核苷酸之雙股斷裂的修復上扮演了關鍵性的角色。2002年在高等植物阿拉伯芥中，發現並分離了古氏-蛋白質的同源蛋白。其單元次體(70千道頓古氏-蛋白質次體和80千道頓古氏-蛋白質次體)與其在人類個體中的同源蛋白質相比較，彼此分子量大小接近，而序列相似性則分別為28.6% 和22.5%。相關的研究指出在去氧核甘酸破壞劑的刺激下，阿拉伯芥古氏-蛋白質扮演了以非同源雙股末端結合途徑，修復去氧核甘酸雙股斷裂的角色。阿拉伯芥古氏-蛋白質在植物中的此類功用，與其同源蛋白質在其他物種中的功用非常相似。如果失去了古氏-蛋白質，則會造成染色體末端長度控制的失調。
在先前古氏-蛋白質基因序列上游啟動子的研究中發現，古氏蛋白質可由植物賀爾蒙和逆境因子所調控。這些內在型和外來型的訊號，有的會激發古氏蛋白質的表現，其他的則會減弱其表現。然而至目前為止，對於古氏蛋白在植物中的調控機制，仍然所知有限。因此在這個研究中，我們嘗試以酵母菌單雜合檢測來探究其分子層次的調控機制。一個被稱作ATAF1的蛋白質，在這次的檢測中被分離出來。已知ATAF1蛋白質會被乾燥和離層酸所誘導。而ATAF1蛋白質作為轉錄調控因子能抑制其他逆境反應基因的表現。綜合ATAF1蛋白質在基因轉錄上的抑制性調控和先前植物賀爾蒙與逆境因子對古氏-蛋白質的影響，我們推測ATAF1蛋白質可能在植物賀爾蒙與逆境因子處理下，扮演基因轉錄的抑制者而減弱古氏-蛋白質的表現。

Ku was first identified as an autoantigen in the sera of patients with autoimmune diseases, as a heterodimer composed of subunits Ku70 and Ku80 that binds to the DNA ends, nicks, or single-to-double-strand transition. Ku plays a crucial role for DNA double-strand-break repair. Homologous of Ku70 and Ku80 in Arabidopsis were identified in 2002, with conserved sizes sharing 28.6 and 22.5% sequence identity with the respective human proteins. Further studies indicated that AtKu plays a similar role in the repair of DNA double-strand breaks by non-homologous end joining (NHEJ) pathway in response to DNA damaging agents in plants as in other organisms. Loss of AtKu results in deregulation of telomere length control.
The previous studies on AtKu promoter activity under treatment of plant hormones and stress indicated that AtKu is regulated by various endogenous and exogenous factors. Some of these signals activate and others inhibit the expression of AtKu. Up to now, the mechanism of the regulation of AtKu in plants still is limited to know.
In this study, we prompted to investigate the molecular mechanism of these processes by yeast one-hybrid screening. A cDNA encoding ATAF1 protein was identified. ATAF1 was reported to be induced by dehydration and ABA, as a transcriptional regulator, to negatively regulate the expression of the other stress responsive genes. To combine results on hormones and stress stimulation with that on the repressor activity of ATAF1 on transcriptional regulation, we speculate that ATAF1 may function as a transcriptional repressor to down regulate the expression of the AtKu genes.

Abe, H., Urao, T., Ito, T., Seki, M., Shinozaki, K. & Yamaguchi-Shinozaki, K. (2003) Arabidopsis AtMYC2 (bHLH) and AtMYB2 (MYB) function as transcriptional activators in abscisic acid signaling. Plant Cell 15: 63–78.
Aida, M., Ishida, T., Fukaki, H., Fujisawa, H. & Tasaka, M. (1997) Genes involved in organ separation in Arabidopsis: an analysis of the cup-shaped cotyledon mutant. Plant Cell 9: 841-857.
Bundock, P., Attikum, H.V. & Hooykaas, P. (2002) Increased telomere length and hypersensitivity to DNA damaging agents in an Arabidopsis KU70 mutant. Nucleic Acids Res. 30: 3395-3400.
Choi, H., Hong, J., Ha, J., Kang, J. & Kim, S.Y. (2000) ABFs, a family of ABA-responsive element binding factors. J Biol Chem. 275: 1723–1730.
Critchlow, S.E. & Jackson, S.P. (1998) DNA end-joining: from yeast to man. Trends Biochem. Sci. 23: 394-398.
Duval, M., Hsieh, T.-F., Kim, S.Y. & Thomas, T.L. (2002) Molecular characterization of AtNAM: a member of the Arabidopsis NAC domain superfamily. Plant Mol. Biol. 50: 237-248.
Dynan, W.S. & Yoo, S. (1998) Interaction of Ku protein and NA-dependent protein kinase catalytic subunit with nucleic acids. Nucleic Acids Res. 26: 1551–1559.
Elledge, S.J., Mulligan, J.T., Ramer, S.W., Spottswood, M. & Davis, R.W. (1991) λYES: A multifunctional cDNA expression vector for the isolation of genes by complementation of yeast and Escherichia coli mutations. Proc. Natl. Acad. Sci. 88: 1731-1735.
Ernst, H.A., Olsen, A.N., Skriver, K., Larsen, S. & Lo Leggio, L.L. (2004) Structure of the conserved domain of ANAC, a member of the NAC family of transcription factors. EMBO Rep. 5: 297-303.
Francouer, A-M., Peebles, C.L., Compper, P.T. & Tan, E.M. (1986) Identification of Ki (Ku, p70/p80) autoantigenes and analysis of anti-Ki autoantibody reactivity. J. Immunol. 136: 1648-1653.
Fujita, M., Fujita, Y,, Maruyama, K., Seki, M., Hiratsu, K., Ohme-Takagi, M., Tran, LS., Yamaguchi-Shinozaki, K. & Shinozaki, K. (2004) A dehydration-induced NAC protein, RD26, is involved in a novel ABA-dependent stress-signaling pathway. Plant J. 39: 863–876.
Gallego, M.E., Jalut, N. & White, C.I. (2003) Telomerase dependence of telomere lengthening in ku80 mutant Arabidopsis. Plant Cell 15: 782-789.
Gstaiger, M., Knoepfel, L., Georgiev, O., Schaffner, W. & Hovens, C.M. (1995) A B-cell coactivator of octamer-binding transcription factors. Nature 373: 360–362.
Harper, J.W., Adami, G.R., Wei, N., Keyomarsi, K. & Elledge, S.J. (1993) The p21 Cdk-interacting protein Cip1 is a potent inhibitor of G1 cyclin-dependent kinases. Cell 75: 805–816.
Iyer, V. & Struhl, K. (1995) Mechanism of differential utilization of the his3 TR and TC TATA elements. Mol. Cell. Biol. 15: 7059-7066.
Kikuchi, K., Ueguchi-Tanaka, M., Yoshida, K.T., Nagato, Y., Matsusoka, M. & Hirano, H.-Y. (2000) Molecular analysis of the NAC gene family in rice. Mol. Gen. Genet. 262: 1047-1051.
Kim, J., Harter, K. & Theologis, A. (1997) Protein-protein interactions among Aux/IAA proteins. Proc.Natl. Acad. Sci. USA 94: 11786-11791.
Lehming, N., Thanos, D., Brickman, J.M., Ma, J., Maniatis, T. & Ptashne, M. (1994) An HMG-like protein that can switch a transcriptional activator to a repressor. Nature 371: 175–179.
Li, J.J. & Herskowitz, I. (1993) Isolation of ORC6, a component of the yeast origin of recognition complex by a one-hybrid system. Science 262: 1870–1873.
Lu, P., Chen, N., An, R., Su, Z., Qi, B., Ren, F., Chen, J. & Wang, X. (2006) A novel drought-inducible gene, ATAF1, encodes a NAC family protein that negatively regulates the expression of stress-responsive genes in Arabidopsis. Plant Mol. Biol. 63: 289–305.
Luo, Y., Vijaychander, S., Stile, J. & Zhu, L. (1996) Cloning and analysis of DNA-binding proteins by yeast one-hybrid and one-two-hybrid systems. Biotechniques 20: 564–568.
Marintchev, A., Mullen, M.A., Maciejewski, M.W., Pan, B., Gryk, M.R. & Mullen, G.P. (1999) Solution structure of the single-strand break repair protein XRCC1 N-terminal domain. Nat. Struct. Biol. 6: 884-893.
Mimori, T., Akizuki, M., Yamagata, H., Inada, S., Yoshida, S. & Homma, M. (1981) Characterization of a high molecular weight acidic nuclear protein recognized by autoantibodies in sera from patients with polymyositis-scleroderma overlap. J. Clin. Invest. 68: 611–620.
Ooka, H., Satoh, K., Doi, K., Nagata, T., Otomo, Y., Murakami, K., Matsubara, K., Osato, N., Kawai, J., Carninci, P., Hayashizaki, Y., Suzuki, K., Kojima, K., Takahara, Y., Yamamoto, K. & Kikuchi, S. (2003) Comprehensive analysis of NAC family genes in Oryza sativa and Arabidopsis thaliana. DNA Res. 10: 239–247.
Riha, K., Watson, J.M., Parkey, J. & Shippen, D.E. (2002) Telomere length deregulation and enhanced sensitivity to genotoxic stress in Arabidopsis mutants deficient in Ku70. EMBO J. 21: 2819-2826.
Shinozaki, K. & Yamaguchi-Shinozaki, K. (2000) Molecular responses to dehydration and low temperature: differences and cross-talk between two stress signaling pathways. Curr Opin Plant Biol. 3: 217–223.
Strubin, M., Newell, J.W. & Matthias, P. (1995) OBF-1, a novel B cell-specific coactivator that stimulates immunoglobin promoter activity through association with octamer-binding proteins. Cell 80: 497–506.
Tamura, K., Adachi, Y., Chiba, K., Oguchi, K. & Takahashi, H. (2002) Identification of Ku70 and Ku80 homologues in Arabidopsis thaliana: evidence for a role in the repair of DNA double strand breaks. The Plant Journal 29: 771-781.
Tran, L.S., Nakashima, K., Sakuma, Y., Simpson, SD., Fujita, Y., Maruyama, K., Fujita, M., Seki, M., Shinozaki, K. & Yamaguchi-Shinozaki, K. (2004) Isolation and functional analysis of Arabidopsis stress-inducible NAC transcription factors that bind to a drought-responsive cis-element in the early responsive to dehydration stress 1 promoter. Plant Cell 16: 2481–2498.
Uno, Y., Furihata, T., Abe, H., Yoshida, R., Shinozaki, K. & Yamaguchi-Shinozaki, K. (2000) Arabidopsis basic leucine zipper transcription factors involved in an abscisic acid-dependent signal transduction pathway under drought and high-salinity conditions. Proc Natl Acad Sci USA 97: 11632–11637.
Wang, M.M. & Reed, R.R. (1993) Molecular cloning of the olfactory neuronal transcription factor Olf-1 by genetic selection in yeast. Nature 364: 121–126.
West, C.E., Waterworth, W.M., Story, G.W., Sunderland, P.A., Jiang, Q. & Bray, C.M. (2002) Disruption of the Arabidopsis AtKu80 gene demonstrates an essential role for AtKu80 protein in efficient repair of DNA double-strand breaks in vivo. Plant J. 31: 517-528.
Xiong, L., Schumaker, K.S. & Zhu, J.K. (2002) Cell signaling during cold, drought, and salt stress. Plant Cell 14(Suppl): S165–183.