Regulation of G1-specific gene expression in yeast

描述（由申请人提供）：真核细胞分裂周期开始时基因表达的控制是大多数细胞类型细胞增殖的起始事件。突变解除了关键的转录开关，导致细胞生长和分裂失控。在人类中，这种调控途径的缺陷与发育障碍和癌症有关。我们建议在出芽酵母中研究类似的转录调控网络，以了解这种调控的本质。超过300个基因在G1期后期协调表达，为进入新的细胞周期做准备。这些基因受到两个相关转录因子SBF和MBF的控制，它们是人类E2F基因家族的功能类似物。这些因子协同作用促进表达，并在细胞进入S期时受到抑制。然而，SBF和MBF受到不同的转录抑制因子的调控，这些转录抑制因子控制着激活和抑制。因此，这两个因子受到细胞和环境信号的不同调节。我们建议在三个特定目的的背景下研究SBF和MBF控制基因表达机制的异同。在第一个目标中，我们将阐明控制MBF靶基因激活的特定调节因子，这是两种转录因子中了解较少的。在第二个目标中，我们将建立细胞退出G1期时MBF靶点的抑制机制。由于转录抑制是该基因网络调控的核心，我们建议应用高分辨率基因组全定位分析来研究转录抑制因子对组蛋白修饰酶及其在核小体上的标记的影响。最后，在第三个目标中，我们将研究SBF和MBF分别受其转录抑制因子wh5和Nrm1差异调控的分子基础，并建立MBF在基因毒性应激诱导DNA复制检查点时规避转录抑制机制的机制。通过对这两种转录因子作用于200多个基因的比较分析，不仅可以对细胞周期调控基因的转录抑制机制有新的认识，而且可以对真核生物中转录抑制的一般作用有新的认识。

DESCRIPTION (provided by applicant): Control of gene expression at the start of the eukaryotic cell division cycle is the initiating event for cell proliferation in most cell types. Mutations deregulating that crucial transcriptional switch lead to uncontrolled cell growth and division. In humans, defects in that regulatory pathway are associated with development disorders and cancer. We propose to study the analogous transcriptional regulatory network in the budding yeast in the interest of understanding the nature of that regulation. Greater than 300 genes are coordinately expressed during late G1 phase in preparation for entry into a new cell cycle. Those genes are under the control of two related transcription factors, SBF and MBF, functional analogs of the E2F gene family in humans. Those factors act coordinately to promote expression and are repressed as cells progress into S phase. However, SBF and MBF are regulated by distinct transcriptional repressors that govern both activation and repression. As a consequence, the two factors are subject to differential regulation by cellular and environmental signals. We propose to study the differences and similarities between the mechanisms governing gene expression controlled by SBF and MBF in the context of three Specific Aims. In the first Aim we will elucidate the specific regulatory factors governing the activation of MBF target genes, the more poorly understood of the two transcription factors. In the second Aim we will establish the mechanism of repression of MBF targets as cells exit G1 phase. Because transcriptional repression is central to the regulation of this gene network, we propose to apply high-resolution genome wide location analysis to study the influence of transcriptional repressors on histone modifying enzymes and their marks on nucleosomes. Finally, in the third Aim we will study the molecular basis for the differential regulation of SBF and MBF by their transcriptional repressors, Whi5 and Nrm1, respectively and establish the mechanism by which MBF evades one mechanism of transcriptional repression when the DNA replication checkpoint is induced by genotoxic stress. The comparative analysis of these two transcription factors acting on more than 200 genes will lead to a new understanding, not only of the mechanisms of transcriptional repression at cell cycle regulated genes, but also on the general role of transcriptional repression in eukaryotes.