Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA.
Microbiology Doctoral Training Program, University of Wisconsin-Madison, Madison, WI 53706, USA.
Nucleic Acids Res. 2018 Feb 28;46(4):1984-1997. doi: 10.1093/nar/gky041.
RNase III is a ribonuclease that recognizes and cleaves double-stranded RNA. Across bacteria, RNase III is involved in rRNA maturation, CRISPR RNA maturation, controlling gene expression, and turnover of messenger RNAs. Many organisms have only one RNase III while others have both a full-length RNase III and another version that lacks a double-stranded RNA binding domain (mini-III). The genome of the cyanobacterium Synechococcus sp. strain PCC 7002 (PCC 7002) encodes three homologs of RNase III, two full-length and one mini-III, that are not essential even when deleted in combination. To discern if each enzyme had distinct responsibilities, we collected and sequenced global RNA samples from the wild type strain, the single, double, and triple RNase III mutants. Approximately 20% of genes were differentially expressed in various mutants with some operons and regulons showing complex changes in expression levels between mutants. Two RNase III's had a role in 23S rRNA maturation and the third was involved in copy number regulation one of six native plasmids. In vitro, purified RNase III enzymes were capable of cleaving some of the known Escherichia coli RNase III target sequences, highlighting the remarkably conserved substrate specificity between organisms yet complex regulation of gene expression.
RNase III 是一种识别并切割双链 RNA 的核糖核酸酶。在细菌中，RNase III 参与 rRNA 成熟、CRISPR RNA 成熟、控制基因表达和信使 RNA 周转。许多生物体只有一种 RNase III，而另一些生物体则既有全长的 RNase III，也有缺少双链 RNA 结合域的另一种版本（mini-III）。蓝藻集胞藻 PCC 7002（PCC 7002）的基因组编码三个 RNase III 同源物，两个全长和一个 mini-III，即使组合缺失也不是必需的。为了辨别每种酶是否具有不同的职责，我们从野生型菌株、单个、双个和三个 RNase III 突变体中收集和测序了全球 RNA 样本。大约 20%的基因在各种突变体中表达不同，一些操纵子和调控子在突变体之间表现出复杂的表达水平变化。两个 RNase III 在 23S rRNA 成熟中起作用，第三个在六个天然质粒之一的拷贝数调节中起作用。在体外，纯化的 RNase III 酶能够切割一些已知的大肠杆菌 RNase III 靶序列，突出了生物体之间底物特异性的惊人保守性，但基因表达的调控却很复杂。
