Jakubowski H
Department of Microbiology and Molecular Genetics, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, Newark 07103.
EMBO J. 1991 Mar;10(3):593-8. doi: 10.1002/j.1460-2075.1991.tb07986.x.
Homocysteine thiolactone is a product of an error-editing reaction, catalyzed by Escherichia coli methionyl-tRNA synthetase, which prevents incorporation of homocysteine into tRNA and protein, both in vitro and in vivo. Here, the thiolactone is also shown to occur in cultures of the yeast Saccharomyces cerevisiae. In yeast, the thiolactone is made from homocysteine in a reaction catalyzed by methionyl-tRNA synthetase. One molecule of homocysteine is edited as thiolactone per 500 molecules of methionine incorporated into protein. Homocysteine, added exogenously to the medium or overproduced by some yeast mutants, is detrimental to cell growth. The cost of homocysteine editing in yeast is minimized by the presence of a pathway leading from homocysteine to cysteine, which keeps intracellular homocysteine at low levels. These results not only directly demonstrate that editing of errors in amino acid selection by methionyl-tRNA synthetase operates in vivo in yeast but also establish the importance of proofreading mechanisms in a eukaryotic organism.
同型半胱氨酸硫内酯是一种错误编辑反应的产物，由大肠杆菌甲硫氨酰 - tRNA合成酶催化，该酶在体外和体内均可防止同型半胱氨酸掺入tRNA和蛋白质中。在此，硫内酯也被证明存在于酿酒酵母的培养物中。在酵母中，硫内酯由同型半胱氨酸在甲硫氨酰 - tRNA合成酶催化的反应中生成。每掺入500个甲硫氨酸分子到蛋白质中，就有一个同型半胱氨酸分子被编辑为硫内酯。向培养基中外源添加同型半胱氨酸或某些酵母突变体过量产生同型半胱氨酸都会对细胞生长有害。酵母中同型半胱氨酸编辑的成本通过存在一条从同型半胱氨酸到半胱氨酸的途径而降至最低，该途径可使细胞内同型半胱氨酸保持在低水平。这些结果不仅直接证明了甲硫氨酰 - tRNA合成酶对氨基酸选择错误的编辑在酵母体内起作用，还确立了真核生物中校对机制的重要性。
