Lill R, Crooke E, Guthrie B, Wickner W
Molecular Biology Institute, University of California, Los Angeles 90024-1570.
Cell. 1988 Sep 23;54(7):1013-8. doi: 10.1016/0092-8674(88)90116-x.
Trigger factor is a soluble, 63,000 dalton protein of E. coli that stabilizes proOmpA, the precursor form of a major outer-membrane protein, in a conformation competent for in vitro membrane assembly. There is approximately one trigger factor molecule bound to each 70S ribosome isolated from cell extracts in physiological buffers. Trigger factor dissociates from ribosomes in 1.5 M LiCl and reassociates with salt-washed ribosomes in low-salt buffer. Binding is exclusively to the 50S (large) subunit, known to contain the exit domain for nascent polypeptide chains. In addition to its associations with proOmpA and ribosomes, excess trigger factor can compete with the proOmpA-trigger factor complex for a limited number of membrane sites that are essential for translocation of proOmpA. These data suggest a model of trigger factor cycling between the cytoplasm, the ribosome, presecretory proteins, and membrane receptor proteins.
触发因子是大肠杆菌中一种可溶性的63000道尔顿蛋白质，它能使主要外膜蛋白的前体形式proOmpA稳定在一种适合体外膜组装的构象中。在生理缓冲液中从细胞提取物中分离出的每个70S核糖体上大约结合有一个触发因子分子。触发因子在1.5M LiCl中从核糖体上解离，并在低盐缓冲液中与盐洗过的核糖体重新结合。它仅与50S（大）亚基结合，已知该亚基包含新生多肽链的出口结构域。除了与proOmpA和核糖体结合外，过量的触发因子可以与proOmpA-触发因子复合物竞争有限数量的对proOmpA转运至关重要的膜位点。这些数据提示了一个触发因子在细胞质、核糖体、分泌前体蛋白和膜受体蛋白之间循环的模型。
