Department of Genetics, University of Georgia, Athens, GA 30605, USA.
Nucleic Acids Res. 2010 Jan;38(2):597-607. doi: 10.1093/nar/gkp997. Epub 2009 Nov 11.
Here we report a unique processing pathway in Escherichia coli for tRNA(Leu5) in which the exoribonuclease polynucleotide phosphorylase (PNPase) removes the Rho-independent transcription terminator from the leuX transcript without requiring the RhlB RNA helicase. Our data demonstrate for the first time that PNPase can efficiently degrade an RNA substrate containing secondary structures in vivo. Furthermore, RNase P, an endoribonuclease that normally generates the mature 5'-ends of tRNAs, removes the leuX terminator inefficiently independent of PNPase activity. RNase P cleaves 4-7 nt downstream of the CCA determinant generating a substrate for RNase II, which removes an additional 3-4 nt. Subsequently, RNase T completes the 3' maturation process by removing the remaining 1-3 nt downstream of the CCA determinant. RNase E, G and Z are not involved in terminator removal. These results provide further evidence that the E. coli tRNA processing machinery is far more diverse than previously envisioned.
在这里，我们报道了大肠杆菌中 tRNA(Leu5)的一种独特加工途径，其中核酸外切酶多核苷酸磷酸化酶（PNPase）在不依赖 RhlB RNA 解旋酶的情况下从 leuX 转录本中去除 Rho 非依赖性转录终止子。我们的数据首次表明，PNPase 可以在体内有效地降解含有二级结构的 RNA 底物。此外，内切核酸酶 RNase P 通常生成 tRNA 的成熟 5'-端，它独立于 PNPase 活性，效率低下地去除 leuX 终止子。RNase P 在 CCA 决定簇下游切割 4-7nt，产生 RNase II 的底物，后者再去除额外的 3-4nt。随后，RNase T 通过去除 CCA 决定簇下游剩余的 1-3nt 完成 3'成熟过程。RNase E、G 和 Z 不参与终止子去除。这些结果进一步证明，大肠杆菌 tRNA 加工机制比以前想象的更加多样化。
