Functional analysis of ribosomes from eukaryotes possessing prokaryotic robosomes.

长期以来，人们一直认为原核糖体和真核糖体在功能和结构上都存在着离散的差异。这些事实影响了真核生物是两种原核细胞融合而产生的概念。最近有报道称，一些寄生原囊具有与原核糖体相似的沉降系数的核糖体。本研究旨在通过分析真核生物核糖体的功能来阐明真核生物的起源。从核糖体沉降系数为70S的家蚕微孢子虫中制备核糖体部分和其他可溶性酶组分。同时制备大鼠肝脏核糖体和大肠杆菌核糖体作为比较。在ATP再生系统中，大肠杆菌和大鼠肝脏核糖体被主动标记苯丙氨酸，依赖于外源添加聚(U)。然而，来自家蚕微孢子虫的核糖体在所考察的任何一个系统中几乎没有标记的氨基酸。改变细胞破碎或细胞分离的方法不能提高系统的活性。在本研究过程中，我们从家蚕核糖体基因组中克隆了包括HSP70基因在内的一些基因。序列分析表明，在生物体的进化过程中，没有线粒体的N.bom bycis是二次丢失线粒体的。

It has long been believed that there are discrete differences between prokaryotic and eukaryotic ribosomes in both function and structure. These facts have influenced on the concept that eukaryotes emerged as a result of fusion of two kinds of prokaryotic cells. Recently, it has been reported that some parasitic procysts possessed ribosomes with sedimentation coefficient similar to prokaryotic ribosomes. This project aimed to elucidate the origin of eukaryote by analyzing the function of the prokaryotic ribosomes from the eukaryotes.Ribosomal fraction and other soluble enzyme fractions were prepared from microsporidia Nosema bombycis whose ribosome has a sedimentation coefficient of 70S.Ribosomes from rat liver and Escherichia coli were also prepared for comparison.With ATP regeneration system, ribosomes from E.coli and rat liver were actively incorporatelabeled phenylalanine depending exogenously added poly(U).Ribosomes from N.bombycis, however, incorporated little, if any, labeled amino acids in any of the system examined.Alteration of cell disrupting or cell fractionation methods failed to improve the activity of the system. We now conclude that the material, i. e., dormant spores of N.bombycis, is not suitable for the source of biologically active ribosomes.During the course of this study, we cloned some genes including HSP7O gene from N.bombycis genome. The sequence analysis revealed that N.bom bycis which does not have mito-chondria lost mitochondria secondarily during the evolution of the organism.