Requirement of Nhp6 proteins for transcription of a subset of tRNA genes and heterochromatin barrier function in Saccharomyces cerevisiae
Requirement of Nhp6 proteins for transcription of a subset of tRNA genes and heterochromatin barrier function in Saccharomyces cerevisiae
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DOI：
10.1128/mcb.00773-06
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发表时间：
2007-03-01
影响因子：
5.3
通讯作者：
Dieci, Giorgio
中科院分区：
文献类型：
--
作者：
Braglia, Priscilla;Dugas, Sandra L.;Dieci, Giorgio
RNA聚合酶（Pol） III转录tRNA基因（tDNA）的一个关键事件是转录起始位点上游TFIIIB依赖于tfiiic的组装。不同的tDNA上游序列以不同的亲和力结合TFIIIB，从而调节tDNA的转录。我们发现，在缺乏Nhp6蛋白的情况下，酿酒酵母5'侧区对tRNA基因转录的影响显著增强。在体内，带有次优TFIIIB结合位点的tDNA的表达强烈依赖于Nhp6，而带有强TFIIIB结合区域的tDNA的表达则不存在。Nhp6对tRNA基因转录的上游序列依赖性刺激可以在体外重现，并且在酵母细胞中发现了与tRNA基因相关的Nhp6蛋白。我们还发现，在没有Nhp6的情况下，HMR位点上的tDNA（Thr）的转录和沉默屏障活性都受到损害。我们的数据表明，Nhp6蛋白是Pol III染色质模板的重要组成部分，它有助于tRNA基因表达的稳健性和Pol III转录复合物的位置效应。
A key event in tRNA gene (tDNA) transcription by RNA polymerase (Pol) III is the TFIIIC-dependent assembly of TFIIIB upstream of the transcription start site. Different tDNA upstream sequences bind TFIIIB with different affinities, thereby modulating tDNA transcription. We found that in the absence of Nhp6 proteins, the influence of the 5'-flanking region on tRNA gene transcription is dramatically enhanced in Saccharomyces cerevisiae. Expression of a tDNA bearing a suboptimal TFIIIB binding site, but not of a tDNA preceded by a strong TFIIIB binding region, was strongly dependent on Nhp6 in vivo. Upstream sequence-dependent stimulation of tRNA gene transcription by Nhp6 could be reproduced in vitro, and Nhp6 proteins were found associated with tRNA genes in yeast cells. We also show that both transcription and silencing barrier activity of a tDNA(Thr) at the HMR locus are compromised in the absence of Nhp6. Our data suggest that Nhp6 proteins are important components of Poll III chromatin templates that contribute both to the robustness of tRNA gene expression and to positional effects of Pol III transcription complexes.