Osumi Y, Imahori K
Proc Natl Acad Sci U S A. 1974 Oct;71(10):4062-6. doi: 10.1073/pnas.71.10.4062.
The mechanism of action of colicin E3 (E3) was investigated in an in vitro system. Purified ribosomes are less susceptible to E3 than crude or washed ribosomes. A factor was found in the supernatant fraction of normal Escherichia coli cells that stimulates inactivation of ribosomes by E3, and on addition of this factor, about one tenth as much E3 was required for inactivation of ribosomes. On heating a mixture of E3 and this factor above 60 degrees , the ribosome inactivating activity of E3 increased greatly, and an amount corresponding to 0.01 mug of E3 was sufficient to inactivate 1.0 A(260) unit of ribosomes completely. By this treatment bacteriocidal activity of E3 decreased considerably, as the ratio of the two activities of E3 (ribosome inactivating activity and bacteriocidal activity) increased to 6 x 10(4)-fold. It is evident that the two activities do not run in parallel. This heat-treated product cleaved 16S rRNA in the same way as E3. These results suggest that inactivation of ribosomes is not due to colicin molecules prepared by the standard procedure, but to a modified form of them.
在体外系统中研究了大肠杆菌素E3（E3）的作用机制。纯化的核糖体比粗制或洗涤过的核糖体对E3的敏感性更低。在正常大肠杆菌细胞的上清液部分发现了一种因子，它能刺激E3对核糖体的失活作用，加入该因子后，使核糖体失活所需的E3量约为原来的十分之一。将E3与该因子的混合物加热至60摄氏度以上时，E3的核糖体失活活性大大增加，相当于0.01微克E3的量就足以使1.0 A（260）单位的核糖体完全失活。通过这种处理，E3的杀菌活性显著降低，因为E3的两种活性（核糖体失活活性和杀菌活性）的比值增加到了6×10⁴倍。显然，这两种活性并非平行变化。这种热处理产物与E3一样能切割16S rRNA。这些结果表明，核糖体的失活不是由于按标准程序制备的大肠杆菌素分子，而是由于它们的一种修饰形式。
