Department of Chemistry and Biochemistry, The University of Maryland, College Park, MD 20742, USA.
Department of Pharmacological Sciences, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA.
Nucleic Acids Res. 2023 Oct 13;51(18):9804-9820. doi: 10.1093/nar/gkad662.
All cells employ a combination of endo- and exoribonucleases to degrade long RNA polymers to fragments 2-5 nucleotides in length. These short RNA fragments are processed to monoribonucleotides by nanoRNases. Genetic depletion of nanoRNases has been shown to increase abundance of short RNAs. This deleteriously affects viability, virulence, and fitness, indicating that short RNAs are a metabolic burden. Previously, we provided evidence that NrnA is the housekeeping nanoRNase for Bacillus subtilis. Herein, we investigate the biological and biochemical functions of the evolutionarily related protein, B. subtilis NrnB (NrnBBs). These experiments show that NrnB is surprisingly different from NrnA. While NrnA acts at the 5' terminus of RNA substrates, NrnB acts at the 3' terminus. Additionally, NrnA is expressed constitutively under standard growth conditions, yet NrnB is selectively expressed during endospore formation. Furthermore, NrnA processes only short RNAs, while NrnB unexpectedly processes both short RNAs and longer RNAs. Indeed, inducible expression of NrnB can even complement the loss of the known global 3'-5' exoribonucleases, indicating that it acts as a general exonuclease. Together, these data demonstrate that NrnB proteins, which are widely found in Firmicutes, Epsilonproteobacteria and Archaea, are fundamentally different than NrnA proteins and may be used for specialized purposes.
所有细胞都采用内切核酸酶和外切核酸酶的组合来降解长的 RNA 聚合物，使其成为 2-5 个核苷酸长度的片段。这些短的 RNA 片段被纳米核糖核酸酶加工成单核糖核苷酸。纳米核糖核酸酶的遗传缺失已被证明会增加短 RNA 的丰度。这会对生存力、毒力和适应性产生有害影响，表明短 RNA 是一种代谢负担。以前，我们提供了证据表明 NrnA 是枯草芽孢杆菌的管家纳米核糖核酸酶。在此，我们研究了进化上相关的蛋白质枯草芽孢杆菌 NrnB（NrnBBs）的生物学和生物化学功能。这些实验表明 NrnB 与 NrnA 惊人地不同。虽然 NrnA 在 RNA 底物的 5' 末端起作用，但 NrnB 在 3' 末端起作用。此外，NrnA 在标准生长条件下持续表达，但 NrnB 仅在芽孢形成期间选择性表达。此外，NrnA 仅处理短 RNA，而 NrnB 出人意料地处理短 RNA 和长 RNA。事实上，诱导表达 NrnB 甚至可以弥补已知的全局 3'-5' 外切核酸酶的缺失，表明它作为一种通用的外切核酸酶发挥作用。总之，这些数据表明，在厚壁菌门、ε变形菌门和古菌中广泛存在的 NrnB 蛋白与 NrnA 蛋白根本不同，可能用于专门目的。
