Giddings T H, Staehelin L A
J Cell Biol. 1980 Apr;85(1):147-52. doi: 10.1083/jcb.85.1.147.
Freeze-fracture micrographs of cells of the green alga Micrasterias denticulata stabilized by ultrarapid freezing reveal imprints of polysomes on the rough endoplasmic reticulum membranes. The imprints appear as broad, spiral ridges on the P faces and as corresponding wide grooves on the E faces of the membranes. Distinct 110-A particles with a spacing of 270 +/- 45 A are associated with the P-face ridges. Where imprints of individual ribosomes can be discerned, it is seen that there is a 1:1 relationship between the ribosomes and the 110-A particles, and that the 110-A particles are located in a peripheral position with respect to the polysome spirals. We propose that the 110-A particles could be structural equivalents of ribosome-binding sites, consisting of a molecule each of ribophorins I and II and a nascent polypeptide chain. These observations suggest that the spiral form of polysomes could result from the forces generated by the extrusion of the growing polypeptide chains to one side of the polysome.
通过超快速冷冻稳定的绿藻齿牙微星藻细胞的冷冻蚀刻显微照片显示,多核糖体在糙面内质网膜上留下印记。这些印记在膜的P面上表现为宽阔的螺旋状脊,在E面上表现为相应的宽槽。间距为270±45 Å的明显的110 Å颗粒与P面脊相关。在可以辨别单个核糖体印记的地方,可以看到核糖体与110 Å颗粒之间存在1:1的关系,并且110 Å颗粒相对于多核糖体螺旋位于外围位置。我们提出,110 Å颗粒可能是核糖体结合位点的结构等效物,由核糖体结合蛋白I和II各一个分子以及一条新生多肽链组成。这些观察结果表明,多核糖体的螺旋形式可能是由生长的多肽链向多核糖体一侧挤出所产生的力导致的。