Deikus Gintaras, Babitzke Paul, Bechhofer David H
Department of Pharmacology and Biological Chemistry, Mount Sinai School of Medicine, New York University, New York, NY 10029, USA.
Proc Natl Acad Sci U S A. 2004 Mar 2;101(9):2747-51. doi: 10.1073/pnas.0307343101. Epub 2004 Feb 19.
When Bacillus subtilis is grown in the presence of excess tryptophan, transcription of the trp operon is regulated by binding of tryptophan-activated TRAP to trp leader RNA, which promotes transcription termination in the trp leader region. Transcriptome analysis of a B. subtilis strain lacking polynucleotide phosphorylase (PNPase; a 3'-to-5' exoribonuclease) revealed a striking overexpression of trp operon structural genes when the strain was grown in the presence of abundant tryptophan. Analysis of trp leader RNA in the PNPase(-) strain showed accumulation of a stable, TRAP-protected fragment of trp leader RNA. Loss of trp operon transcriptional regulation in the PNPase(-) strain was due to the inability of ribonucleases other than PNPase to degrade TRAP-bound leader RNA, resulting in the sequestration of limiting TRAP. Thus, in the case of the B. subtilis trp operon, specific ribonuclease degradation of RNA in an RNA-protein complex is required for recycling of an RNA-binding protein. Such a mechanism may be relevant to other systems in which limiting concentrations of an RNA-binding protein must keep pace with ongoing transcription.
当枯草芽孢杆菌在过量色氨酸存在的情况下生长时，色氨酸激活的TRAP与trp前导RNA结合可调节trp操纵子的转录，这会促进trp前导区域的转录终止。对缺乏多核苷酸磷酸化酶（PNPase；一种3'至5'外切核糖核酸酶）的枯草芽孢杆菌菌株进行转录组分析发现，当该菌株在丰富的色氨酸存在下生长时，trp操纵子结构基因显著过表达。对PNPase（-）菌株中的trp前导RNA进行分析，结果显示trp前导RNA有一个稳定的、受TRAP保护的片段积累。PNPase（-）菌株中trp操纵子转录调控的丧失是由于除PNPase之外的核糖核酸酶无法降解与TRAP结合的前导RNA，从而导致有限的TRAP被隔离。因此，就枯草芽孢杆菌trp操纵子而言，RNA-蛋白质复合物中RNA的特异性核糖核酸酶降解是RNA结合蛋白循环利用所必需的。这种机制可能与其他系统相关，在这些系统中，RNA结合蛋白的有限浓度必须与正在进行的转录保持同步。
