Sykes J, Metcalf E, Pickering J D
J Gen Microbiol. 1977 Jan;98(1):17-27. doi: 10.1099/00221287-98-1-17.
The 'relaxed particles' formed during methionine starvation of Escherichia coli A19 (Hfr rel met rns) have been isolated by large-scale rate-zonal density gradient ultracentrifugation. The proteins and rRNA species associated with these particles have been examined. The rRNA species present are precursor and mature forms of 16S and 23S rRNA. The bulk of the rRNA which accumulates during starvation is found within the particles. The proteins prepared directly from the particles give strong multiple immunoprecipitates with antisera specific to 30S and 50S ribosomal proteins. The soluble proteins, prepared and examined in the same manner, do not give this immunological reaction. Two-dimensional electrophoresis patterns of the proteins from the particles show that the proteins co-migrate with proteins from 30S and 50S ribosomes and are entirely dissimilar to the proteins prepared by the same methods from the soluble fraction of the cells. On the basis of these and other observations, it is concluded that the 'relaxed particles' are not artefacts but are arrested ribosome precursors containing both rRNA and certain ribosomal proteins. The free pool of ribosomal proteins is low in exponential-phase cells and is not significantly increased by a 2 h period of starvation for glucose. The implications of these observations concerning the proteins associated with 'relaxed' and 'chloramphenicol particles' are discussed in raltion to ribosome biogenesis and the stabilization of rRNA.
通过大规模速率区带密度梯度超速离心法，分离出了在大肠杆菌A19（高频重组株rel met rns）蛋氨酸饥饿期间形成的“松弛颗粒”。已对与这些颗粒相关的蛋白质和rRNA种类进行了检测。存在的rRNA种类为16S和23S rRNA的前体和成熟形式。饥饿期间积累的大部分rRNA存在于颗粒中。直接从颗粒中制备的蛋白质与针对30S和50S核糖体蛋白的抗血清产生强烈的多重免疫沉淀反应。以相同方式制备和检测的可溶性蛋白质则不会产生这种免疫反应。颗粒中蛋白质的二维电泳图谱表明，这些蛋白质与30S和50S核糖体中的蛋白质共同迁移，并且与通过相同方法从细胞可溶性部分制备的蛋白质完全不同。基于这些及其他观察结果，得出结论：“松弛颗粒”并非人为产物，而是包含rRNA和某些核糖体蛋白的停滞核糖体前体。核糖体蛋白的游离库在指数生长期细胞中含量较低，并且在饥饿2小时的葡萄糖条件下并未显著增加。本文结合核糖体生物发生和rRNA的稳定性，讨论了这些观察结果对于与“松弛颗粒”和“氯霉素颗粒”相关蛋白质的意义。
