Burenina O Y, Elkina D A, Hartmann R K, Oretskaya T S, Kubareva E A
Lomonosov Moscow State University, Chemistry Department, Moscow, 119991, Russia.
Biochemistry (Mosc). 2015 Nov;80(11):1429-46. doi: 10.1134/S0006297915110048.
Small noncoding RNAs (ncRNAs) are non-translated transcripts with lengths below 300 nucleotide residues. Regulation of cellular processes under the influence of these ncRNAs is the most various in eukaryotic cells, but numerous ncRNAs are also found in bacteria. One of the best-known small prokaryotic ncRNAs is 6S RNA - it has been detected in all branches of bacteria. Due to their conserved secondary structure including a large central "loop" flanked by long double-helical arms, 6S RNAs can bind holoenzymes of RNA polymerase (RNAP) and inhibit their activity. This inhibits transcription of many genes. According to data of comparative transcriptome analysis, the 6S RNA-dependent regulation of transcription affects the expression level of hundreds of genes involved in various cellular processes. 6S RNA has the unique feature of serving as a transcription template for the synthesis of short product RNAs (pRNAs) complementary to the central part of the molecule. The length and abundance of pRNAs vary depending on the physiological status of the cell. The synthesis of pRNAs is of great importance because it releases RNAP and provides reversibility of the inhibition. A similar mechanism has been described for the noncoding mouse B2 RNA that inhibits the activity of RNAP II. This finding can be taken as evidence for the common evolutionary origin of the ncRNA-dependent regulation of RNAP and its immense significance for cells. This review summarizes the state of knowledge about the main features and functions of 6S RNAs from various bacterial species with a special focus on the peculiarities of pRNA synthesis. The majority of functional insights on 6S RNAs have been gained for E. coli 6S RNA as the best-studied model system.
小非编码RNA（ncRNA）是长度低于300个核苷酸残基的非翻译转录本。在这些ncRNA的影响下，真核细胞中细胞过程的调控最为多样，但在细菌中也发现了大量的ncRNA。最著名的小原核ncRNA之一是6S RNA——它已在细菌的所有分支中被检测到。由于其保守的二级结构，包括一个被长双螺旋臂侧翼的大中心“环”，6S RNA可以结合RNA聚合酶（RNAP）的全酶并抑制其活性。这抑制了许多基因的转录。根据比较转录组分析的数据，6S RNA依赖的转录调控影响了参与各种细胞过程的数百个基因的表达水平。6S RNA具有独特的功能，即作为合成与分子中心部分互补的短产物RNA（pRNA）的转录模板。pRNA的长度和丰度因细胞的生理状态而异。pRNA的合成非常重要，因为它释放了RNAP并提供了抑制作用的可逆性。对于抑制RNAP II活性的非编码小鼠B2 RNA也描述了类似的机制。这一发现可以作为ncRNA依赖的RNAP调控的共同进化起源及其对细胞的巨大意义的证据。本综述总结了关于来自各种细菌物种的6S RNA的主要特征和功能的知识状态，特别关注pRNA合成的特点。作为研究最充分的模型系统，对大肠杆菌6S RNA已经获得了大多数关于6S RNA的功能见解。
