Torres Martha, Balada Joan-Miquel, Zellars Malcolm, Squires Craig, Squires Catherine L
King Faisal Specialist Hospital and Research Centre, Radiation Biology Laboratory, Biomedical Physics Department, Riyadh 11211, Saudi Arabia.
J Bacteriol. 2004 Mar;186(5):1304-10. doi: 10.1128/JB.186.5.1304-1310.2004.
Similarities between lambda and rRNA transcription antitermination have led to suggestions that they involve the same Nus factors. However, direct in vivo confirmation that rRNA antitermination requires all of the lambda Nus factors is lacking. We have therefore analyzed the in vivo role of NusB and NusG in rRNA transcription antitermination and have established that both are essential for it. We used a plasmid test system in which reporter gene mRNA was measured to monitor rRNA antiterminator-dependent bypass of a Rho-dependent terminator. A comparison of terminator read-through in a wild-type Escherichia coli strain and that in a nusB::IS10 mutant strain determined the requirement for NusB. In the absence of NusB, antiterminator-dependent terminator read-through was not detected, showing that NusB is necessary for rRNA transcription antitermination. The requirement for NusG was determined by comparing rRNA antiterminator-dependent terminator read-through in a strain overexpressing NusG with that in a strain depleted of NusG. In NusG-depleted cells, termination levels were unchanged in the presence or absence of the antiterminator, demonstrating that NusG, like NusB, is necessary for rRNA transcription antitermination. These results imply that NusB and NusG are likely to be part of an RNA-protein complex formed with RNA polymerase during transcription of the rRNA antiterminator sequences that is required for rRNA antiterminator-dependent terminator read-through.
λ噬菌体与核糖体RNA（rRNA）转录抗终止之间的相似性引发了一种观点，即它们涉及相同的Nus因子。然而，目前缺乏rRNA抗终止需要所有λ噬菌体Nus因子的直接体内证据。因此，我们分析了NusB和NusG在rRNA转录抗终止中的体内作用，并确定它们对此过程均至关重要。我们使用了一种质粒测试系统，通过测量报告基因mRNA来监测rRNA抗终止子依赖的对Rho依赖型终止子的通读情况。通过比较野生型大肠杆菌菌株和nusB::IS10突变菌株中的终止子通读情况，确定了对NusB的需求。在缺乏NusB的情况下，未检测到抗终止子依赖的终止子通读，这表明NusB是rRNA转录抗终止所必需的。通过比较过表达NusG的菌株和NusG缺失的菌株中rRNA抗终止子依赖的终止子通读情况，确定了对NusG的需求。在NusG缺失的细胞中，无论有无抗终止子，终止水平均未改变，这表明NusG与NusB一样，是rRNA转录抗终止所必需的。这些结果表明，NusB和NusG可能是在rRNA抗终止子序列转录过程中与RNA聚合酶形成的RNA - 蛋白质复合物的一部分，该复合物是rRNA抗终止子依赖的终止子通读所必需的。
