Moehring J M, Moehring T J, Danley D E
Proc Natl Acad Sci U S A. 1980 Feb;77(2):1010-4. doi: 10.1073/pnas.77.2.1010.
We have identified two types of mutants of Chinese hamster ovary cells in which the unique ADP-ribose attachment site in elongation factor 2 (EF-2) is altered, thereby rendering them resistant to diphtheria and Pseudomonas toxins (TOXR). The first is mutant in the gene for EF-2 and possesses a permanently altered, TOXR gene product. The second lacks a component of a posttranslational modification system that converts TOXR EF-2 to the toxin-sensitive (TOXS) state. We postulate that this modification system is involved in the conversion of a single histidine residue in EF-2 to the specific target of toxin-catalyzed ADP-ribosylation, the novel amino acid X. We have designated the second type MOD- mutants. The missing of nonfunctional component in the MOD- mutants can be restored by hybridizing them with either normal TOXS cells or with EF-2 structural gene mutants. The TOXR EF-2 from MOD- mutants is also converted to toxin sensitivity in vitro by incubation with extracts of TOXS or EF-2 gene mutant cells in the presence of an energy-generating system. Our results demonstrate that EF-2 can be synthesized and released from ribosomes in a toxin-resistant form and then converted to toxin sensitivity by posttranslational modification.
我们已经鉴定出中国仓鼠卵巢细胞的两种突变体，其中延伸因子2（EF-2）中独特的ADP-核糖附着位点发生了改变，从而使它们对白喉毒素和铜绿假单胞菌毒素（TOXR）具有抗性。第一种是EF-2基因的突变体，拥有一种永久改变的TOXR基因产物。第二种缺乏将TOXR EF-2转化为毒素敏感（TOXS）状态的翻译后修饰系统的一个成分。我们推测这种修饰系统参与将EF-2中的单个组氨酸残基转化为毒素催化的ADP-核糖基化的特定靶标，即新的氨基酸X。我们将第二种类型命名为MOD-突变体。MOD-突变体中缺失的无功能成分可以通过将它们与正常的TOXS细胞或EF-2结构基因突变体杂交来恢复。在有能量产生系统存在的情况下，将MOD-突变体的TOXR EF-2与TOXS或EF-2基因突变体细胞的提取物一起孵育，也可在体外将其转化为毒素敏感性。我们的结果表明，EF-2可以以抗毒素形式从核糖体合成并释放出来，然后通过翻译后修饰转化为毒素敏感性。
