自人類及多種生物的基因體被解碼後，生命科學界立即邁向後基因體時代，而基因功能及蛋白質體學成為研究重點。學者們常有機會因為由某個生物體的genome之序列中找到的功能未知基因而需要面對必須找出該基因所轉譯出的蛋白質之生物學功能的挑戰。找出新基因產物之功能的方法就如同是去了解生命系統的組成。 啤酒酵母菌（Saccharomyces cerevisiae）中的 YHR209W 基因又被稱為 CRG1，被認為是參與調節抵抗斑蝥素（cantharidin）的相關作用的基因。由於 YHR209W 也具有甲基轉移酶之特徵序列，而 YHR209W 基因所轉譯出的蛋白質經由蛋白質序列比對（Blast-P）發現與許多甲基轉移酶較為相似且具有形成與S-腺苷甲硫胺酸（S-adenosyl-L-methionine，AdoMet；簡稱為SAM）結合之三級結構部位的序列，因此 YHR209Wp 被推測為可能具有甲基轉移酶之活性。 在本研究中為了探討 YHR209W 是否具有甲基轉移酶之活性以及探討其可能的受質，我們將啤酒酵母菌中的 YHR209W 基因構築到大腸桿菌（Escherichia coli; E. coli ) 之中使其表現出重組蛋白 YHR209Wp ，再以已剔除 YHR209W 基因的啤酒酵母菌 lysate為受質，利用具有放射線性質的 S-腺苷甲硫胺酸作為輔基質來測定重組蛋白 YHR209Wp 之活性。 Since the genome of human and other creatures has been decoded, the life science gets into the post-genomic era, and the gene functions and proteomics become the main research areas. Researchers often have chances to face the challenge of the protein bio-function translated by a function unknown gene found in the genome of an organism. Methods to find out the functions of new gene’s products are as to realize the components of the life system. YHR209W, also called CRG1, has been known to be involved in mediating cantharidin resistance of Saccharomysec cereviseae. YHR209W has been inferred as a methyltransferase by sequence comparison, and the Protein translated by YHR209W is called Yhr209wp. Because Yhr209wp is similar with many methyltransferases in Blast-P, and has S-adenosyl-L-methionine binding domain sequence, YHR209W is a putative S-adenosylmethionine-dependent methyltransferase. In order to confirm if YHR209W has methyltransferase activity and possible substrate, in this research, we construct the yeast YHR209W gene into E. coli (Escherichia coli) in different host cell strains and conditions to express the recombinant protein Yhr209wp. The activity is determined by a reaction containing Yhr209wp, protein substrates ΔYHR209W yeast genome and cosubstrate isotope labeled S-adenosyl-L-methionine.
