Mehlin H, Daneholt B, Skoglund U
Department of Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institutet, Stockholm, Sweden.
J Cell Biol. 1995 Jun;129(5):1205-16. doi: 10.1083/jcb.129.5.1205.
The transport of Balbiani ring (BR) premessenger RNP particles in the larval salivary gland cells of the dipteran Chironomus tentans can be followed using electron microscopy. A BR RNP particle consists of an RNP ribbon bent into a ringlike structure. Upon translocation through the nuclear pore complex (NPC), the ribbon is straightened and enters the central channel of the NPC with the 5' end of the transcript in the lead. The translocating ribbon is likely to interact with the central channel but, in addition, the remaining portion of the ribbon ring makes contact with the periphery of the NPC. To determine the nature of this latter interaction, we have now studied the connections between the RNP particle and the border of the NPC during different stages of translocation using electron microscope tomography. It was observed that the 3' terminal domain of the ribbon always touches the nuclear ring of the NPC, but the precise area of contact is variable. Sometimes also a region on the opposite side of the ribbon ring reaches the nuclear ring. The pattern of contacts could be correlated to the stage of translocation, and it was concluded that the particle-nuclear ring interactions reflect a rotation of the ribbon ring in front of the central channel, the rotation being secondary to the successive translocation of the ribbon through the channel. The particle's mode of interaction with the NPC suggests that the initial contact between the 5' end domain of the ribbon and the entrance to the central channel is probably crucial to accomplish the ordered translocation of the premessenger RNP particle through the NPC.
利用电子显微镜可以追踪双翅目昆虫摇蚊幼虫唾液腺细胞中巴尔比亚尼环（BR）前信使核糖核蛋白颗粒的运输过程。一个BR核糖核蛋白颗粒由一条弯曲成环状结构的核糖核蛋白带组成。在通过核孔复合体（NPC）转运时，核糖核蛋白带会伸直，并以转录本的5'端在前进入NPC的中央通道。转运中的核糖核蛋白带可能会与中央通道相互作用，但除此之外，核糖核蛋白带环的其余部分会与NPC的周边接触。为了确定这种后者相互作用的性质，我们现在使用电子显微镜断层扫描技术研究了转运不同阶段核糖核蛋白颗粒与NPC边界之间的连接。观察到核糖核蛋白带的3'末端结构域总是接触NPC的核环，但精确的接触区域是可变的。有时核糖核蛋白带环另一侧的一个区域也会到达核环。接触模式可能与转运阶段相关，并且得出结论，颗粒 - 核环相互作用反映了核糖核蛋白带环在中央通道前的旋转，这种旋转是核糖核蛋白带依次通过通道转运的结果。颗粒与NPC相互作用的方式表明，核糖核蛋白带的5'端结构域与中央通道入口之间的初始接触可能对于前信使核糖核蛋白颗粒通过NPC的有序转运至关重要。
