蛋白質的後修飾作用(post-translational modification)包含了甲基化(methylation)、磷酸化(phosphorylation)…等。在生物體內某些蛋白分子之胺基酸在合成過程中可以被甲基化，如:組織胺酸(histidine)、離胺酸(lysine)和精胺酸(arginine)，這些甲基化反應多半是不可逆的，但有可能是可被調控的，且往往在某些生理反應上扮演著重要的作用。在本論文中，我的實驗目的，是為了想去了解酵母菌(Saccharomyces cerevisiae)內分子量約略為七萬的熱休克蛋白(Ssa1p及Ssa2p)甲基化之狀況。我發現在正常的生長狀況下，熱休克蛋白(Ssa1p及Ssa2p)中某些離胺酸(lysine)和精胺酸(arginine)可以被甲基化。因此我試著想找出其甲基化的酵素(AdoMet-dependent methyltransferases)，在一些實驗後，發現Ynl092wp可能是Ssa1p或Ssa2p的甲基化酵素(methyltransferases)。接著我利用雙突變菌種(double deletion strain)來探討這一課題。結果發現Ynl092wp並非Ssa1p的甲基化酵素。很不幸的，我們並沒有得到 ssa1Δynl092wΔ的雙突變種(double deletion strain)，因此Ynl092wp是否為Ssa2p的甲基化酵素(methyltransferases)則不得而之。而Ssa1p和Ssa2p甲基化所扮演的作用亦不得而知，推測Ssa1p和Ssa2p的甲基化可能與生物體內的調節或是和反應基質(substrate)之間的相互作用力有著重要的關係。

Protein methylation is one of the post-translational modifications that may have important function. The basic amino acid residues such as histidine, lysine, and arginine can be methylated in vivo; and the methylation on basic amino acid appears irreversible and coupled to protein synthesis. In this study, I characterized the methylation of the 70-KDa heat shock proteins (Ssa1p and Ssa2p) in Saccharomyces cerevisiae. I showed that Ssa1p and Ssa2p were methylated in cells grown under normal conditions. The Ssa1p and Ssa2p are methylated on lysine as well as arginine residue(s). I also intended to identify the Ssa1p and Ssa2p-specific S-adenosylmethionine (AdoMet)-dependent methyl-transferases. On first trial, it appeared that Ynl092wp might be responsible for the methylation of Ssa1p or Ssa2p. Then, the double deletion strain was generated for further study. It is clear that Ynl092wp was not a Ssa1p-specific methyltransferase. However, the ssa1Δ ynl092wΔ double mutant was not obtained. Thus, it remains to be determined if Ynl092wp is a methyltransferase responsible for the methylation of Ssa2p. Moreover, biological functions of methylated Ssa1p and Ssa2p need to been determined. It might have important function in cell regulation or substrate interaction.

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