Transcriptional Regulation in Yeast Genomic Chromatin

本项目旨在阐明酵母减数分裂早期基因染色质改变的转录调控机制。酿酒酵母进入减数分裂的过程受环境信号和一系列调控基因的调控。IME1和IME2（减数分裂诱导剂）基因产物在决定是否启动减数分裂中起关键作用。在无法进入减数分裂的单倍体细胞中，Rme1p抑制IME1，而在营养细胞中，Ume6p与组蛋白去乙酰化酶Rpd3p复合物抑制IME2。在这项研究中，我们研究了Rme1p和Ume6p-Rpd3p在体内的抑制机制。我们证明了Rme1p在体内远距离阻止激活子与其靶位点结合以发挥抑制作用，并提出Rme1p可能建立了一个局部的抑制染色质结构域。另一方面，研究表明激活剂的靶位点存在于Ume6p-Rpd3p抑制的启动子中。这些结果不能用一个广泛提出的模型来解释，即组蛋白乙酰化-去乙酰化调节核小体结构以调节反式作用因子的结合。此外，我们发现TBP （TATA box binding protein）的人工募集绕过了Ume6p-Rpd3p的抑制，这表明组蛋白去乙酰化离子抑制了TBP的结合和/或RNA聚合酶II全酶的募集。总之，我们提出了Rme1p和Ume6p-Rpd3p与染色质相关的抑制机制。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是进化保守的。

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.