Hershko A, Ganoth D, Pehrson J, Palazzo R E, Cohen L H
Unit of Biochemistry, Faculty of Medicine, Technion-Israel Institute of Technology, Haifa.
J Biol Chem. 1991 Sep 5;266(25):16376-9.
A derivative of ubiquitin in which amino groups were blocked by reductive methylation was used to study the possible role of the ubiquitin pathway in the cell cycle-programmed degradation of cyclin. It was shown previously that methylated ubiquitin can be efficiently ligated to protein substrates, but cannot form polyubiquitin chains. In the well-characterized ubiquitin-dependent proteolytic system from reticulocytes, it was found that rates of protein breakdown obtained with methylated ubiquitin are generally slower than those with ubiquitin; and thus, this derivative can be used, in some cases, as an inhibitor of ubiquitin-dependent protein degradation. The addition of methylated ubiquitin to a cell-free system from fertilized clam oocytes inhibited the degradation of both cyclins A and B. That this was due to specific interference with ubiquitin function was indicated by the observation that the supplementation of excess ubiquitin completely overcame the inhibitory action of methylated ubiquitin on cyclin degradation. These findings suggest that polyubiquitin chain formation is required for cyclin degradation.
一种通过还原甲基化使氨基被封闭的泛素衍生物被用于研究泛素途径在细胞周期程序化的细胞周期蛋白降解中可能发挥的作用。先前已表明，甲基化的泛素能够有效地与蛋白质底物连接，但无法形成多聚泛素链。在已得到充分研究的网织红细胞中依赖泛素的蛋白水解系统中，发现用甲基化泛素获得的蛋白质分解速率通常比用泛素时要慢；因此，在某些情况下，这种衍生物可用作泛素依赖性蛋白质降解的抑制剂。向受精蛤卵母细胞的无细胞系统中添加甲基化泛素会抑制细胞周期蛋白A和B的降解。观察到补充过量的泛素能完全克服甲基化泛素对细胞周期蛋白降解的抑制作用，这表明这是由于对泛素功能的特异性干扰所致。这些发现表明细胞周期蛋白降解需要多聚泛素链的形成。
