Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Apartado 127, Oeiras, Portugal.
Wiley Interdiscip Rev RNA. 2011 Nov-Dec;2(6):818-36. doi: 10.1002/wrna.94. Epub 2011 Jul 6.
RNAs are important effectors in the process of gene expression. In bacteria, constant adaptation to environmental demands is accompanied by a continual adjustment of transcripts' levels. The cellular concentration of a given RNA is the result of the balance between its synthesis and degradation. RNA degradation is a complex process encompassing multiple pathways. Ribonucleases (RNases) are the enzymes that directly process and degrade the transcripts, regulating their amounts. They are also important in quality control of RNAs by detecting and destroying defective molecules. The rate at which RNA decay occurs depends on the availability of ribonucleases and their specificities according to the sequence and/or the structural elements of the RNA molecule. Ribosome loading and the 5'-phosphorylation status can also modulate the stability of transcripts. The wide diversity of RNases present in different microorganisms is another factor that conditions the pathways and mechanisms of RNA degradation. RNases are themselves carefully regulated by distinct mechanisms. Several other factors modulate RNA degradation, namely polyadenylation, which plays a multifunctional role in RNA metabolism. Additionally, small non-coding RNAs are crucial regulators of gene expression, and can directly modulate the stability of their mRNA targets. In many cases this regulation is dependent on Hfq, an RNA binding protein which can act in concert with polyadenylation enzymes and is often necessary for the activity of sRNAs. All of the above-mentioned aspects are discussed in the present review, which also highlights the principal differences between the RNA degradation pathways for the two main Gram-negative and Gram-positive bacterial models.
RNAs 是基因表达过程中的重要效应因子。在细菌中，对环境需求的持续适应伴随着转录本水平的持续调整。特定 RNA 的细胞浓度是其合成和降解平衡的结果。RNA 降解是一个复杂的过程，包括多个途径。核糖核酸酶 (RNases) 是直接处理和降解转录本的酶，调节其数量。它们在 RNA 质量控制中也很重要，通过检测和破坏有缺陷的分子。RNA 衰变的速度取决于核糖核酸酶的可用性及其根据 RNA 分子的序列和/或结构元件的特异性。核糖体加载和 5'-磷酸化状态也可以调节转录本的稳定性。不同微生物中存在的广泛多样性的 RNases 是另一个影响 RNA 降解途径和机制的因素。RNases 本身通过不同的机制进行精细调节。其他几个因素也可以调节 RNA 降解，例如多聚腺苷酸化，它在 RNA 代谢中具有多种功能。此外，小非编码 RNA 是基因表达的关键调节剂，它们可以直接调节其 mRNA 靶标稳定性。在许多情况下，这种调节依赖于 Hfq，一种 RNA 结合蛋白，它可以与多聚腺苷酸化酶协同作用，并且通常是 sRNAs 活性所必需的。本综述讨论了所有上述方面，还强调了两种主要革兰氏阴性和革兰氏阳性细菌模型的 RNA 降解途径之间的主要差异。
