Moss T, Larose A M, Mitchelson K, Leblanc B
Centre de recherche en cancérologie de l'Université Laval, Hôtel-Dieu de Québec, Canada.
Biochem Cell Biol. 1992 May;70(5):324-31. doi: 10.1139/o92-050.
An RNA polymerase I termination site is found just upstream of the ribosomal gene promoter in mammals and amphibia. It has been suggested that this termination site may actively enhance ribosomal transcription in a process known as readthrough enhancement or that it may simply prevent the disruption of initiation complexes or promoter occlusion. There is, however, a consensus of opinion that the terminator is important for efficient ribosomal transcription. Here we have quantitatively investigated the relative importance of readthrough enhancement and promoter occlusion on the transcription of the microinjected Xenopus laevis ribosomal gene. The results show that, in this system, promoter occlusion is limited and terminator mutations predominantly affect readthrough enhancement. The terminator is shown to be unnecessary for the enhancer activity of the rest of the ribosomal spacer. Model calculations suggest that readthrough enhancement could be explained by polymerase recycling and that it may be unnecessary to postulate a specific mechanism of polymerase handover.
在哺乳动物和两栖动物中，核糖体基因启动子上游紧邻着一个RNA聚合酶I终止位点。有人提出，这个终止位点可能在一个被称为通读增强的过程中积极促进核糖体转录，或者它可能只是防止起始复合物的破坏或启动子阻塞。然而，人们普遍认为终止子对高效核糖体转录很重要。在这里，我们定量研究了通读增强和启动子阻塞对显微注射的非洲爪蟾核糖体基因转录的相对重要性。结果表明，在这个系统中，启动子阻塞是有限的，终止子突变主要影响通读增强。结果显示，终止子对于核糖体间隔区其余部分的增强子活性并非必需。模型计算表明，通读增强可以用聚合酶循环来解释，而且可能没有必要假定一种特定的聚合酶交接机制。
