Chromatin Modification and Pre-Messenger RNA Splicing

自2001年公布人类基因组序列以来，很明显，了解基因组的下一步是回答一些基本问题：“基因组中包含的信息是如何表达的，每个基因的正确表达是如何控制的？”基因组的两个特征使这成为一个特别有趣的问题。首先，人类基因（以及其他真核生物的基因）被非编码DNA序列的长片段打断。一旦DNA被细胞机器“读取”并转录成“信使RNA”（一种指导蛋白质合成的含有中间信息的遗传物质），这些非编码RNA的长链必须被移除，剩下的蛋白质编码区域必须被连接起来。这种细胞过程，“前信使RNA剪接”，发生得非常精确，对正确的基因表达至关重要。基因组的第二个显著特征是DNA被包裹在一种叫做染色质的紧密的蛋白质/DNA结构中。为了使DNA序列转录成信使RNA，染色质必须经过广泛的修饰，改变DNA的包装，使DNA可接近。这种DNA可及性的变化在调节RNA合成中起着关键作用。虽然涉及基因表达的反应通常是作为孤立的过程独立研究的，但最近的研究表明，RNA合成和剪接实际上是紧密协调的：剪接反应发生在RNA合成的同时。因此，RNA合成反应可以影响剪接过程，而pre-mRNA剪接可以影响RNA合成。鉴于前mrna剪接和RNA合成之间的这些联系，人们可能会期望RNA合成机制导航染色质结构和合成信使RNA的能力与剪接机制协调去除内含子之间的联系。本项目将利用生物化学和遗传上易于处理的模式生物——酵母酿酒酵母，通过分析前mrna剪接机制与染色质修饰和染色质重组机制之间的协调关系，探索基因表达的基本机制。

Since the 2001 announcement of the sequence of the human genome, it has become evident that the next step toward understanding the genome is answering the fundamental questions: "How does the information contained within the genome get expressed, and how is the correct expression of each gene controlled?" Two features of the genome make this a particularly intriguing problem. First, human genes (and genes from other eukaryotic organisms) are interrupted by long stretches of non-coding DNA sequence. Once the DNA is "read" by the cellular machinery and transcribed to make "messenger RNA" (the intermediate information-containing genetic material that directs protein synthesis), these long stretches of non-coding RNA must be removed, and the remaining protein-coding regions must be joined. This cellular process, "pre-messenger RNA splicing," takes place with exquisite accuracy and is crucial for proper gene expression. The second notable feature of the genome is that the DNA is packaged in a compact protein/DNA structure called chromatin. In order for the DNA sequence to be transcribed to make messenger RNA, the chromatin must undergo extensive modification that alters the DNA packaging and makes the DNA accessible. This change in DNA accessibility plays a pivotal role in regulating RNA synthesis. While the reactions involved in gene expression have typically been studied independently, as isolated processes, recent studies have illustrated that RNA synthesis and splicing are, in fact, tightly coordinated: the splicing reaction occurs as the RNA is being synthesized. Consequently, the RNA synthesis reaction can affect the process of splicing, and pre-mRNA splicing can affect RNA synthesis. Given these connections between pre-mRNA splicing and RNA synthesis, one might expect connections between the RNA synthesis machinery's ability to navigate chromatin structure and synthesize messenger RNA, and the coordinated removal of introns by the splicing machinery. Using the biochemically and genetically tractable model organism, the yeast Saccharomyces cerevisiae, this project will explore the basic mechanisms underlying gene expression by analyzing the coordination between the pre-mRNA splicing machinery and the chromatin modifying and chromatin restructuring machineries.