Transcriptional Regulation in Yeast Genomic Chromatin

本项目的目的是阐明酿酒酵母早期减数分裂基因通过染色质改变进行转录调控的机制。酿酒酵母进入减数分裂的过程既受环境信号的调控，又受一系列调控基因的调控。IME1和IME2(减数分裂诱导物)基因产物在决定启动减数分裂的过程中起着关键作用。Rme1p在不能进入减数分裂的单倍体细胞中抑制IME1，而Ume6p与组蛋白脱乙酰酶Rpd3p结合在营养细胞中抑制IME2。在本研究中，我们研究了Rme1p和Ume6p-Rpd3p在体内的抑制机制。我们证明了Rme1p在体内远距离起作用，阻止激活剂与其靶部位结合以施加抑制，并提出Rme1p可能建立了一个局部的抑制性染色质结构域。另一方面，发现激活子存在于被Ume6p-Rpd3p抑制的启动子中。这些结果不能用广泛提出的组蛋白乙酰化-去乙酰化调节核小体结构来调节反式作用因子结合的模型来解释。此外，我们还发现TBP(TATA盒结合蛋白)的人工募集绕过了Ume6p-Rpd3p的抑制，这表明组蛋白脱乙酰基抑制了TBP的结合和/或RNA聚合酶II全酶的募集。综上所述，我们提出了Rme1p和Ume6p-Rpd3p与染色质相关的新的抑制机制。这些发现可能与所有真核细胞相关，因为这里研究的转录因子在进化上是保守的。

The purpose of this project is to elucidate mechanisms of transcriptional regulation through chromatin alteration in early meiotic genes in yeast Saccharomyces cerevisiae. The process of entering meiosis in S. cerevisiae is regulated by both environmental signals and a cascade of regulatory genes. The IME1 and IME2 (Inducer of meiosis) gene products play a pivotal role in the decision to initiate meiosis. Rme1p represses IME1 in haploid cells, which are unable to enter meiosis, whereas Ume6p complexed with histone deacetylase Rpd3p represses IME2 in vegetative cells. In this study, we examined mechanisms of repression by Rme1p and Ume6p-Rpd3p in vivo. We demonstrated that Rme1p acts at a distance to prevent activators from binding to their target sites to exert repression in vivo, and proposed that Rme1p may establish a localized repressive chromatin domain. On the other hand, it was shown that activators is present their target sites in promoters repressed by Ume6p-Rpd3p. These results can not be explained by a model proposed widely that histone acetylation-deacetylation modulates the nucleosome structure to regulate trans-acting factor binding. Furthermore, we found that an artificial recruitment of TBP (TATA box binding protein) bypasses repression by Ume6p-Rpd3p, suggesting that histone deacetylarion inhibits TBP binding and/or recruitment of RNA polymerase II holoenzyme. In summery, we proposed novel mechanisms for repression by Rme1p and Ume6p-Rpd3p in relation to chromatin. These findings may be relevant for all eukaryotic cells, since transcription factors studied here are evolutionarily conserved.