The fate of ribosomes in Escherichia coli cells starved for a carbon source.
The fate of ribosomes in Escherichia coli cells starved for a carbon source.
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DOI：
10.1016/s0021-9258(19)41773-0
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发表时间：
1975-03
期刊：
影响因子：
--
通讯作者：
Ruth Kaplani;D. Apirion
中科院分区：
文献类型：
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作者：
Ruth Kaplani;D. Apirion
研究了缺乏碳源的大肠杆菌细胞中核糖体的消失。我们使用了一系列突变体，其中一些缺乏核糖核酸酶 I（RNase I，EC 2.7.7.17），另一些则含有修饰的多核苷酸磷酸化酶（PNPase，EC 2.7.7.8）和修饰的核糖核酸酶 II（RNase II，EC 3.1.4.1）的各种组合。从饥饿的突变细胞中制备 RNA，并在聚丙烯酰胺凝胶上分离。获得的结果表明，23S RNA 的降解在所有缺乏 RNase I 的菌株中是相似的，并且在含有该酶的菌株中略有增加。所有测试菌株中 16 S RNA 降解的程度都是相同的。大小为 4 S 或更小的 RNA 种类在含有修饰形式的 PNPase 和 RNase II 的突变体中积累。在所有含有未修饰 RNase II 的菌株中均观察到出现比 16 S RNA (d16 S RNA) 小 10% 的 RNA 种类。对核糖体和多聚体及其 RNA 含量的分析表明，多聚体转化为单体，而单体又转化为核糖体亚基。多核糖体、70 S、OR 50 C颗粒中未发现RNA降解产物； 30 S 亚基包含 16 S RNA 以及 d16 S RNA 种类。在所有缺乏 RNase I 的菌株中，亚基的降解程度相似，而在含有 RNase I 的菌株中，亚基的降解速度稍快。从饥饿细胞制备的亚基中，RNA 与蛋白质的比例与未饥饿培养物相似。在碳饥饿期间，这些突变体中核糖体蛋白的降解非常少。从降解核糖体释放的蛋白质存在于快速沉淀（20,000 倍克）的沉淀中。细胞活力研究表明突变体从饥饿中恢复的能力与其降解 RNA 的能力之间存在直接相关性。因此，暗示了饥饿期间核糖体降解的生物学必要性。基于这些数据，我们提出核糖体 RNA 的核酸内切降解是饥饿降解的主要事件。它发生在核糖体亚基中，核糖体亚基在核糖核酸内切攻击后分解。这种切割产生的 RNA 片段被 RNase II 和 PNPase 降解为核苷酸。核糖体蛋白附着在细胞膜上。
The disappearance of ribosomes in Escherichia coli cells starved for a carbon source was studied. We used a series of mutants, some of them lacking in ribonuclease I(RNase I, EC 2.7.7.17), and other containing various combinations of modified polynucleotide phosphorylase (PNPase, EC 2.7.7.8) and modified ribonuclease II (RNase II, EC 3.1.4.1). RNA was prepared from the starved mutant cells and separated on polyacrylamide gels. The results obtained indicate that 23 S RNA degradation is similar in all strains that lack RNase I, and is slightly increased in the strain that contains this enzyme. The extent of 16 S RNA degradation is identical in all strains tested. RNA species in the size of 4 S and smaller accumulate in mutants containing modified forms of PNPase and RNase II. The appearance of an RNA species 10% smaller than 16 S RNA (d16 S RNA) was observed in all strains that contain unmodified RNase II. Analysis of ribosomes and polysomes and their RNA content indicated that polysomes are converted to monosomes and these, in turn, to ribosomal subunits. No RNA degradation products were found in polysomes, 70 S, OR 50 C particle; 30 S subunits contained 16 S RNA as well as the d16 S RNA species. Subunits are degraded to a similar extent in all strains lacking RNase I, and at a slightly faster rate in the strain that contains RNase I. The RNA to protein ratio in subunits prepared from starved cells is similar to that of unstarved cultures. Very little degradation of ribosomal proteins occurs in these mutants during carbon starvation. The proteins released from degraded ribosomes are found in the fast sedimenting (20,000 times g) pellet. Cell viability studies indicated a direct correlation between the capacity of the mutants to recovery from starvation and their capacity to degrade RNA. Thus a biological necessity for degradation of ribosomes during starvation is implied. Based on these data we propose that the endonucleolytic degradation of ribosomal RNA is the primary event in starvation degradation. It takes place in ribosomal subunits, which fall apart after the endonucleoltic attack. The RNA pieces produced by this cleavage are degraded to nucleotide by RNase II and PNPase. The ribosomal proteins attach to the cell membrane.