To adapt to a wide range of nutritional and environmental changes, cells must adjust their gene expression profiles. This process is completed by the frequent transcription and rapid degradation of mRNA. mRNA decay is initiated by a series of endo- and exoribonucleases. These enzymes leave behind 2- to 5-nt-long oligoribonucleotides termed “nanoRNAs” that are degraded by specific nanoRNases; the degradation of nanoRNA is essential because nanoRNA can mediate the priming of transcription initiation that is harmful for the cell via an unknown mechanism. Identified nanoRNases include Orn in E. coli, NrnA and NrnB in B. subtilis, and NrnC in Bartonella. Even though these nanoRNases can degrade nanoRNA specifically into mononucleotides, the biochemical features, structural features and functional mechanisms of these enzymes are different. Sequence analysis has identified homologs of these nanoRNases in different bacteria, including Gammaproteobacteria, Betaproteobacteria, Alphaproteobacteria, Firmicutes and Cyanobacteria. However, there are several bacteria, such as those belonging to the class Thermolithobacteria, that do not have homologs of these nanoRNases. In this paper, the source of nanoRNA, the features of different kinds of nanoRNases and the distribution of these enzymes in prokaryotes are described in detail.

为了适应各种营养和环境变化，细胞必须调整其基因表达谱。此过程通过mRNA的频繁转录和快速降解来完成。mRNA衰减是由一系列内切和外切核糖核酸酶引发的。这些酶留下了被特异的nanoRNases降解的2至5 nt长的寡核苷酸，称为“ nanoRNA”。纳米RNA的降解至关重要，因为纳米RNA可以通过未知机制介导对细胞有害的转录起始。鉴定出的nanoRNase包括大肠杆菌中的Orn，枯草芽孢杆菌中的NrnA和NrnB以及巴尔通体中的NrnC。即使这些nanoRNase可以将nanoRNA特异性降解为单核苷酸，但这些酶的生化特征，结构特征和功能机制是不同的。序列分析已鉴定出这些纳米RNA酶在不同细菌中的同源物，所述不同细菌包括γ-变形杆菌，β-变形杆菌，α-变形杆菌，硬毛和蓝细菌。但是，有几种细菌（例如属于嗜热石蜡菌的细菌）没有这些nanoRNase的同源物。本文详细描述了nanoRNA的来源，不同种类的nanoRNase的特征以及这些酶在原核生物中的分布。