Department of Biochemistry and Molecular Biology, Miller School of Medicine, University of Miami, Miami, Florida 33101, USA.
RNA. 2012 Jan;18(1):37-41. doi: 10.1261/rna.030213.111. Epub 2011 Nov 28.
RNase R is a processive exoribonuclease that plays an important role in degradation of structured RNAs in Escherichia coli. RNase R is unstable in exponential phase cells; however, under certain stress conditions, RNase R levels increase dramatically due to its stabilization. Binding of tmRNA and SmpB to the C-terminal region of RNase R is required for its instability, and this binding is regulated by acetylation of a single residue, Lys544, in exponential phase cells. RNase R is not acetylated in stationary phase. We show here that only exponential phase RNase R is acetylated because the modifying enzyme, protein lysine acetyltransferase, Pka (YfiQ), is absent from late exponential and stationary phase cells. As a consequence, newly synthesized RNase R remains unmodified. Together with the turnover of preexisting acetylated RNase R, no modified RNase R remains in stationary phase. We find that RNase R in cold-shocked cells also lacks the acetyl modification due to the absence of Pka. These data indicate that RNase R stability depends on Pka, which itself is regulated under stress conditions.
RNase R 是一种具有顺式作用的核酸外切酶，在大肠杆菌中对结构 RNA 的降解起着重要作用。RNase R 在指数生长期细胞中不稳定；然而，在某些应激条件下，由于其稳定性的增加，RNase R 水平会显著增加。tmRNA 和 SmpB 与 RNase R 的 C 末端区域结合对于其不稳定性是必需的，这种结合受到指数生长期细胞中单个残基 Lys544 乙酰化的调节。在稳定期细胞中，RNase R 不被乙酰化。我们在这里表明，只有指数生长期的 RNase R 被乙酰化，因为修饰酶，即蛋白赖氨酸乙酰转移酶 Pka（YfiQ），不存在于指数生长期和稳定期的细胞中。因此，新合成的 RNase R 保持未修饰状态。与现有乙酰化 RNase R 的周转率一起，稳定期没有修饰的 RNase R 残留。我们发现，由于 Pka 的缺失，冷休克细胞中的 RNase R 也缺乏乙酰化修饰。这些数据表明，RNase R 的稳定性取决于 Pka，而 Pka 本身是在应激条件下受到调节的。
