Masaki Haruhiko, Ogawa Tetsuhiro
Department of Biotechnology, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan.
Biochimie. 2002 May-Jun;84(5-6):433-8. doi: 10.1016/s0300-9084(02)01425-6.
Colicins E5 and D cleave the anticodon loops of distinct tRNAs of Escherichia coli both in vivo and in vitro, which accounts for their bactericidal actions through depletion of tRNAs and prevention of protein synthesis. The targets of colicin E5 are five tRNA species for four amino acids, tyrosine, histidine, asparagine and aspartic acid, and those of colicin D are four isoaccepting tRNAs for arginine. These two colicins represent a new class, the "tRNase-type", of the nuclease-type colicins, which previously comprised the DNase-type and ribotoxin-type (or rRNase-type). On the other hand, a certain clinical E. coli strain produces a potentially suicidal "anticodon-nuclease", PrrC, in response to phage T4 infection, which specifically cleaves its own lysine tRNA. For these three tRNases, i.e. colicins E5 and D, and PrrC, the substrates and reaction products, as well as their physiological consequences, are very similar to each other, but so many molecular features are different that these three proteins are assumed to have acquired similar functions through evolutionary convergence from different origins.
大肠杆菌素E5和D在体内和体外均能切割大肠杆菌不同tRNA的反密码子环，这解释了它们通过消耗tRNA和阻止蛋白质合成而产生的杀菌作用。大肠杆菌素E5的靶标是四种氨基酸（酪氨酸、组氨酸、天冬酰胺和天冬氨酸）对应的五种tRNA，而大肠杆菌素D的靶标是精氨酸对应的四种同功tRNA。这两种大肠杆菌素代表了核酸酶型大肠杆菌素中的一个新类别，即“tRNase型”，以前的核酸酶型大肠杆菌素包括DNase型和核糖毒素型（或rRNase型）。另一方面，某临床大肠杆菌菌株在受到噬菌体T4感染时会产生一种潜在的自杀性“反密码子核酸酶”PrrC，它能特异性切割自身的赖氨酸tRNA。对于这三种tRNase，即大肠杆菌素E5和D以及PrrC，它们的底物、反应产物及其生理后果彼此非常相似，但它们的许多分子特征却不同，因此推测这三种蛋白质是通过不同起源的进化趋同而获得了相似的功能。
