Department of Microbiology and Cell Biology, Indian Institute of Science, Bengaluru, 560012, India.
Institute of Bioinformatics and Applied Biotechnology, Bengaluru, 560100, India.
Biochem Biophys Res Commun. 2020 Jan 29;522(1):226-232. doi: 10.1016/j.bbrc.2019.11.062. Epub 2019 Nov 20.
In Escherichia coli, G/C-rich hairpin structure followed by a U-tract in the 3' region of the nascent RNA are crucial determinants for intrinsic or factor independent transcription termination. In mycobacteria, there is a scarcity of such intrinsic terminators. However, secondary structures having G/C-rich stem devoid of any U's or with suboptimal U-tracts were identified earlier as terminators and found to be functional both in vitro and in vivo. Two different observations - that a mycobacterial RNA polymerase (RNAP) does not function at intrinsic terminators devoid of U-tracts and the identification of an altogether new motif for termination in mycobacteria necessitated re-examining a number of putative terminators for their function as terminators. When these in silico identified non-canonical terminators were subjected to experimental validation, they were found to dissociate RNA from the elongating RNAP. Termination is observed when the U-tracts were reduced, or totally absent both in vitro and in vivo. Our results, thus indicate that the presence of U-tract following the G/C-rich stem in an intrinsic terminator may not be an essential determinant for transcription termination in mycobacteria.
在大肠杆菌中，新生 RNA 3' 区域中富含 G/C 的发夹结构和 U 型区是内在或无因子依赖转录终止的关键决定因素。在分枝杆菌中，这种内在终止子稀缺。然而，之前已经确定了具有富含 G/C 的茎且没有任何 U 的二级结构或具有非最佳 U 型区作为终止子，并且在体外和体内均具有功能。有两个不同的观察结果 - 一种分枝杆菌 RNA 聚合酶 (RNAP) 不能在没有 U 型区的内在终止子上发挥作用，以及在分枝杆菌中鉴定出一种全新的终止子 motif，这使得有必要重新检查许多假定的终止子作为终止子的功能。当对这些通过计算机识别的非典型终止子进行实验验证时，发现它们会使 RNA 从延伸的 RNAP 上解离。当 U 型区减少或在体外和体内完全缺失时，就会观察到终止。因此，我们的结果表明，在内在终止子中富含 G/C 的茎后存在 U 型区可能不是分枝杆菌转录终止的必要决定因素。
