Kendall A, Hull M W, Bertrand E, Good P D, Singer R H, Engelke D R
Department of Biological Chemistry and Program in Cellular and Molecular Biology, University of Michigan, Ann Arbor, MI 48109-0606, USA.
Proc Natl Acad Sci U S A. 2000 Nov 21;97(24):13108-13. doi: 10.1073/pnas.240454997.
In the budding yeast, Saccharomyces cerevisiae, actively transcribed tRNA genes can negatively regulate adjacent RNA polymerase II (pol II)-transcribed promoters. This tRNA gene-mediated silencing is independent of the orientation of the tRNA gene and does not require direct, steric interference with the binding of either upstream pol II factors or the pol II holoenzyme. A mutant was isolated in which this form of silencing is suppressed. The responsible point mutation affects expression of the Cbf5 protein, a small nucleolar ribonucleoprotein protein required for correct processing of rRNA. Because some early steps in the S. cerevisiae pre-tRNA biosynthetic pathway are nucleolar, we examined whether the CBF5 mutation might affect this localization. Nucleoli were slightly fragmented, and the pre-tRNAs went from their normal, mostly nucleolar location to being dispersed in the nucleoplasm. A possible mechanism for tRNA gene-mediated silencing is suggested in which subnuclear localization of tRNA genes antagonizes transcription of nearby genes by pol II.
在出芽酵母酿酒酵母中，活跃转录的tRNA基因可对相邻的RNA聚合酶II（Pol II）转录的启动子产生负调控作用。这种tRNA基因介导的沉默作用与tRNA基因的方向无关，且不需要对上游Pol II因子或Pol II全酶的结合进行直接的空间干扰。分离出了一个突变体，其中这种沉默形式受到抑制。导致该突变的点突变影响了Cbf5蛋白的表达，Cbf5蛋白是rRNA正确加工所需的一种小核仁核糖核蛋白。由于酿酒酵母前体tRNA生物合成途径中的一些早期步骤发生在核仁中，我们研究了CBF5突变是否可能影响这种定位。核仁稍有碎片化，前体tRNA从其正常的、大多位于核仁的位置分散到核质中。由此提出了一种tRNA基因介导的沉默作用的可能机制，即tRNA基因的亚核定位拮抗Pol II对附近基因的转录。
