Institute for Genetics; University of Cologne; Cologne, Germany.
RNA Biol. 2012 Jan;9(1):98-109. doi: 10.4161/rna.9.1.18228. Epub 2012 Jan 1.
Hyper-osmotic stress strongly induces expression of the Escherichia coli proU operon encoding a high affinity uptake system for the osmoprotectants glycine betaine and proline betaine. Osmoregulation of proU takes place at the transcriptional level by upregulation of the promoter at high osmolarity and repression of transcription by the nucleoid-associated protein H-NS at low osmolarity. In the present study, we describe an additional level of proU osmoregulation that is independent of transcriptional regulation. We show that osmoregulation occurs at a post-transcriptional level involving RNase III. RNase III specifically processes the proU mRNA within a conserved secondary structure extending from position +203 to +293 of the transcript. Processing is efficient at low osmolarity, but inhibited at high osmolarity. Blocking of RNase III processing by mutation of the processing site eliminates post-transcriptional osmoregulation of proU. Further, the proU mRNA is relatively stable at high osmolarity with a half-life of approximately 65 sec. However, upon osmotic downshift, RNase III immediately processes the proU mRNA which reduces its half-life to less than 4 sec. The data suggest that the primary role of RNase III-mediated processing of proU mRNA is to ensure rapid shutdown of proU upon hypo-osmotic stress.
高渗胁迫强烈诱导编码高亲和力摄取系统的大肠杆菌 proU 操纵子的表达，用于渗透压保护剂甘氨酸甜菜碱和脯氨酸甜菜碱。proU 的渗透压调节发生在转录水平，通过在高渗透压时上调启动子和在低渗透压时由核相关蛋白 H-NS 抑制转录来实现。在本研究中，我们描述了 proU 渗透压调节的另一个独立于转录调节的水平。我们表明，在涉及核糖核酸酶 III 的转录后水平上发生渗透压调节。核糖核酸酶 III 特异性地在从转录物的+203 到+293 位的保守二级结构内处理 proU mRNA。在低渗透压下，处理效率高，但在高渗透压下受到抑制。通过突变处理位点阻断核糖核酸酶 III 处理消除了 proU 的转录后渗透压调节。此外，在高渗透压下，proU mRNA 相对稳定，半衰期约为 65 秒。然而，在渗透下降时，核糖核酸酶 III 立即处理 proU mRNA，使其半衰期缩短至不到 4 秒。数据表明，核糖核酸酶 III 介导的 proU mRNA 加工的主要作用是确保在低渗透压胁迫下迅速关闭 proU。
