Ibrahimi I
J Cell Biol. 1987 Jan;104(1):61-6. doi: 10.1083/jcb.104.1.61.
The translocation of prepromelittin (pPM) across mammalian endoplasmic reticulum was studied in both wheat germ and reticulocyte lysate. In the wheat germ system, signal recognition particle (SRP) caused a transient arrest in the synthesis of pPM. This was indicated by a slowdown in the rate of synthesis of pPM in the presence of SRP. The arrest was specific, dependent on the concentration of SRP, and more effective at early incubation time. In a tightly synchronized translation system, SRP had no apparent effect on the elongation of pPM, indicating that the effect of SRP on pPM chain synthesis might be at the final stages of chain elongation and release from the ribosome. This was reflected in a transient accumulation of pPM as peptidyl tRNA. Because pPM is composed of only 70 amino acids, arrest by SRP may be very close to chain termination. Arrest at this stage of chain synthesis seems to be unstable and the nascent chain gets terminated and released from the ribosome after a transient delay. The translocation of pPM was shown to be dependent on both SRP and docking protein. The difference in the translocation efficiency of pPM in reticulocyte and wheat germ lysates may reflect a difference in the targeting process in the two systems.
在麦胚和网织红细胞裂解物中研究了前催乳素原（pPM）跨哺乳动物内质网的转运。在麦胚系统中，信号识别颗粒（SRP）导致pPM合成短暂停滞。这表现为在存在SRP的情况下pPM合成速率减慢。这种停滞是特异性的，取决于SRP的浓度，并且在孵育早期更有效。在一个紧密同步的翻译系统中，SRP对pPM的延伸没有明显影响，这表明SRP对pPM链合成的作用可能在链延伸和从核糖体释放的最后阶段。这表现为pPM作为肽基tRNA的短暂积累。由于pPM仅由70个氨基酸组成，SRP引起的停滞可能非常接近链终止。在链合成的这个阶段的停滞似乎是不稳定的，新生链在短暂延迟后从核糖体终止并释放。已证明pPM的转运依赖于SRP和对接蛋白。pPM在网织红细胞和麦胚裂解物中的转运效率差异可能反映了这两个系统中靶向过程的差异。
