Pietromonaco S F, Denslow N D, O'Brien T W
Department of Biochemistry and Molecular Biology, University of Florida College of Medicine, Gainesville 32610.
Biochimie. 1991 Jun;73(6):827-35. doi: 10.1016/0300-9084(91)90062-6.
The bovine mitochondrial system is being developed as a model system for studies on mammalian mitochondrial ribosomes. Information is emerging on the structural organization and RNA binding properties of proteins in these mitochondrial ribosomes. Unexpectedly, these ribosomes appear to interact directly with GTP, via a high affinity binding site on the small subunit. Despite major differences in their RNA content and physical properties, mammalian mitochondrial and cytoplasmic ribosomes contain about the same number of proteins. The proteins in each kind of ribosome have a similar size distribution, and both sets are entirely coded by nuclear genes, raising the possibility that these different ribosomes may contain the same set of proteins. Comparison of bovine mitochondrial and cytoplasmic r-proteins by co-electrophoresis in two-dimensional gels reveals that most of the cytoplasmic ribosomal proteins are more basic than the mitochondrial ribosomal proteins, and that none are co-migratory with mitochondrial ribosomal proteins, suggesting that the proteins in the two ribosomes are different. To exclude the possibility that the electrophoretic differences result only from post-translational modification of otherwise identical proteins, antibodies against several proteins from the large subunit of bovine mitochondrial ribosomes were tested against cytoplasmic ribosomes by solid phase radioimmunoassay and against cytoplasmic ribosomal proteins on Western blots. The lack of cross-reaction of these antibodies with cytoplasmic r-proteins suggests that mitochondrial ribosomal proteins have different primary structures and thus are most likely encoded by a separate set of nuclear genes.
牛线粒体系统正被开发为研究哺乳动物线粒体核糖体的模型系统。关于这些线粒体核糖体中蛋白质的结构组织和RNA结合特性的信息正在不断涌现。出乎意料的是，这些核糖体似乎通过小亚基上的高亲和力结合位点直接与GTP相互作用。尽管哺乳动物线粒体核糖体和细胞质核糖体在RNA含量和物理性质上存在重大差异，但它们所含蛋白质的数量大致相同。每种核糖体中的蛋白质具有相似的大小分布，并且两组蛋白质均完全由核基因编码，这增加了这些不同核糖体可能包含相同蛋白质组的可能性。通过二维凝胶中的共电泳比较牛线粒体和细胞质核糖体蛋白，结果表明，大多数细胞质核糖体蛋白比线粒体核糖体蛋白的碱性更强，并且没有一种与线粒体核糖体蛋白共迁移，这表明两种核糖体中的蛋白质是不同的。为了排除电泳差异仅由原本相同的蛋白质的翻译后修饰导致的可能性，通过固相放射免疫测定法针对细胞质核糖体以及在蛋白质免疫印迹中针对细胞质核糖体蛋白，测试了针对牛线粒体核糖体大亚基中几种蛋白质的抗体。这些抗体与细胞质核糖体蛋白缺乏交叉反应，这表明线粒体核糖体蛋白具有不同的一级结构，因此很可能由一组单独的核基因编码。
