UMR 8261 (CNRS-Univ. Paris Diderot, Sorbonne Paris Cité), Institut de Biologie Physico-Chimique, 13 rue Pierre et Marie Curie, 75005 Paris, France.
Nucleic Acids Res. 2018 Sep 19;46(16):8605-8615. doi: 10.1093/nar/gky488.
Ribosomal RNAs are processed from primary transcripts containing 16S, 23S and 5S rRNAs in most bacteria. Maturation generally occurs in a two-step process, consisting of a first crude separation of the major species by RNase III during transcription, followed by precise trimming of 5' and 3' extensions on each species upon accurate completion of subunit assembly. The various endo- and exoribonucleases involved in the final processing reactions are strikingly different in Escherichia coli and Bacillus subtilis, the two best studied representatives of Gram-negative and Gram-positive bacteria, respectively. Here, we show that the one exception to this rule is the protein involved in the maturation of the 3' end of 16S rRNA. Cells depleted for the essential B. subtilis YqfG protein, a homologue of E. coli YbeY, specifically accumulate 16S rRNA precursors bearing 3' extensions. Remarkably, the essential nature of YqfG can be suppressed by deleting the ribosomal RNA degrading enzyme RNase R, i.e. a ΔyqfG Δrnr mutant is viable. Our data suggest that 70S ribosomes containing 30S subunits with 3' extensions of 16S rRNA are functional to a degree, but become substrates for degradation by RNase R and are eliminated.
核糖体 RNA 是从含有 16S、23S 和 5S rRNA 的初级转录本中加工而来的，大多数细菌都是如此。成熟过程通常分两步进行，包括转录过程中 RNase III 对主要物种的初步粗分离，以及亚基组装完成后对每个物种的 5' 和 3' 延伸进行精确修剪。涉及最终加工反应的各种内切核酸酶和外切核酸酶在革兰氏阴性菌 Escherichia coli 和革兰氏阳性菌 Bacillus subtilis 中差异显著，这两种菌是研究最深入的革兰氏阴性菌和革兰氏阳性菌代表。在这里，我们表明，这一规则的一个例外是参与 16S rRNA 3' 端成熟的蛋白质。枯草芽孢杆菌必需蛋白 YqfG 缺失的细胞（E. coli YbeY 的同源物），特别积累带有 3' 延伸的 16S rRNA 前体。值得注意的是，YqfG 的必需性质可以通过删除核糖体 RNA 降解酶 RNase R 来抑制，即 ΔyqfG Δrnr 突变体是可行的。我们的数据表明，含有 16S rRNA 3' 延伸的 30S 亚基的 70S 核糖体在一定程度上是有功能的，但会成为 RNase R 降解的底物，并被消除。
