Caulfield M P, Horiuchi S, Tai P C, Davis B D
Proc Natl Acad Sci U S A. 1984 Dec;81(24):7772-6. doi: 10.1073/pnas.81.24.7772.
The 64-kDa membrane protein of Bacillus subtilis is evidently involved in the attachment of secreting ribosomes to membrane. On immunoprecipitation with antibody to this protein, the solubilized particulate fraction, with or without prior chemical cross-linking, yields a complex of four proteins (64, 60, 41, and 36 kDa). This "S complex" was found to be associated with membrane-free ribosomes rather than with membrane, but the 64-kDa protein is also present, without the other proteins of the S complex, in the membrane-ribosome fraction and in the cytosol. Only the form present in the membrane-ribosome fraction is protected from protease. These findings suggest a cycle in which the complex participates in initiation of secretion but not in the later stages. It is not yet clear whether the 64-kDa protein found in the membrane-ribosome complexes is retained from the S complex after initiation and later recycled via the cytosol or whether it is a separate pool.
枯草芽孢杆菌的64 kDa膜蛋白显然参与分泌核糖体与膜的附着。用针对该蛋白的抗体进行免疫沉淀时，无论有无事先化学交联，溶解的颗粒部分都会产生四种蛋白（64、60、41和36 kDa）的复合物。发现这种“S复合物”与无膜核糖体相关，而非与膜相关，但64 kDa蛋白也存在于膜 - 核糖体部分和胞质溶胶中，且没有S复合物的其他蛋白。只有存在于膜 - 核糖体部分的形式受到蛋白酶的保护。这些发现表明存在一个循环，其中该复合物参与分泌起始但不参与后期阶段。目前尚不清楚在膜 - 核糖体复合物中发现的64 kDa蛋白是在起始后从S复合物保留下来并随后通过胞质溶胶循环利用，还是它是一个单独的储备库。
