Transcriptional Regulation in Yeast Genomic Chromatin

本研究的目的是阐明酿酒酵母减数分裂早期基因染色质改变的转录调控机制。S.酿酒酵母是由环境信号和调控基因级联调控。IME 1和IME 2（减数分裂诱导因子）基因产物在决定减数分裂启动中起关键作用。Rme 1 p抑制单倍体细胞中的IME 1，其不能进入减数分裂，而Ume 6p与组蛋白脱乙酰酶Rpd 3 p复合抑制营养细胞中的IME 2。在这项研究中，我们研究了Rme 1 p和Ume 6p-Rpd 3 p在体内的抑制机制。我们证明，Rme 1 p的作用在一定的距离，以防止激活剂结合到他们的靶位点，在体内施加抑制，并提出Rme 1 p可能建立一个本地化的抑制染色质结构域。另一方面，显示激活剂在被Ume 6p-Rpd 3 p阻遏的启动子中存在其靶位点。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以调节反式作用因子结合的模型来解释。此外，我们发现TBP（TATA盒结合蛋白）的人工募集绕过Ume 6p-Rpd 3 p的抑制，这表明组蛋白去乙酰化抑制TBP结合和/或RNA聚合酶II全酶的募集。总之，我们提出了新的机制，抑制Rme 1 p和Ume 6p-Rpd 3 p染色质。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.