Redundant mechanisms are used by Ssn6-Tup1 in repressing chromosomal gene transcription in Saccharomyces cerevisiae
Redundant mechanisms are used by Ssn6-Tup1 in repressing chromosomal gene transcription in Saccharomyces cerevisiae
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DOI：
10.1074/jbc.m407159200
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发表时间：
2004-09-17
影响因子：
4.8
通讯作者：
Reese, JC
中科院分区：
文献类型：
--
作者：
Zhang, Z;Reese, JC
Ssn 6-Tup 1辅阻遏物复合物调节酿酒酵母中的许多基因。目前已提出三种机制来解释其抑制功能：1）通过结合组蛋白尾部定位核小体; 2）募集组蛋白去乙酰化酶; 3）直接干扰一般转录机器或激活剂。目前尚不清楚Ssn 6-Tup 1是否以冗余方式在单个基因上利用这些机制中的每一种，或者在不同的基因座上单独利用这些机制中的每一种。在一个天然启动子的每种机制的贡献的系统分析还没有报道。在这里，我们采用了一种遗传策略来分析核小体定位，组蛋白去乙酰化和介体干扰在体内抑制染色体Tup 1靶基因的贡献。我们利用了这样一个事实，即Ssn 6-Tup 1需要ISW 2染色质重塑复合物来建立体内核小体定位，以破坏染色质结构而不影响其他Tup 1抑制功能。删除ISW 2，组蛋白脱乙酰酶基因HDA 1，或编码介体亚基的基因单独引起RNR 3和HUG 1的轻微或无去抑制。然而，当介体突变与Deltaisw 2或Deltahda 1突变组合时，观察到增强的转录，并且在三重Deltaisw 2/Deltahda 1/介体突变体中观察到最强水平的去阻遏。突变体中转录的增加不是由于Tup 1在启动子处的丢失，而是与TBP与启动子的交联增加相关。因此，Tup 1利用多种冗余机制来抑制天然基因的转录，这对于它在各种启动子处充当全局辅阻遏物可能是重要的。
The Ssn6-Tup1 corepressor complex regulates many genes in Saccharomyces cerevisiae. Three mechanisms have been proposed to explain its repression functions: 1) nucleosome positioning by binding histone tails; 2) recruitment of histone deacetylases; and 3) direct interference with the general transcription machinery or activators. It is unclear if Ssn6-Tup1 utilizes each of these mechanisms at a single gene in a redundant manner or each individually at different loci. A systematic analysis of the contribution of each mechanism at a native promoter has not been reported. Here we employed a genetic strategy to analyze the contributions of nucleosome positioning, histone deacetylation, and Mediator interference in the repression of chromosomal Tup1 target genes in vivo. We exploited the fact that Ssn6-Tup1 requires the ISW2 chromatin remodeling complex to establish nucleosome positioning in vivo to disrupt chromatin structure without affecting other Tup1 repression functions. Deleting ISW2, the histone deacetylase gene HDA1, or genes encoding Mediator subunits individually caused slight or no derepression of RNR3 and HUG1. However, when Mediator mutations were combined with Deltaisw2 or Deltahda1 mutations, enhanced transcription was observed, and the strongest level of derepression was observed in triple Deltaisw2/Deltahda1/Mediator mutants. The increased transcription in the mutants was not due to the loss of Tup1 at the promoter and correlated with increased TBP cross-linking to promoters. Thus, Tup1 utilizes multiple redundant mechanisms to repress transcription of native genes, which may be important for it to act as a global corepressor at a wide variety of promoters.