Copy number control of the yeast plasmid

酵母质粒2微米环为自私基因组（或良性分子寄生虫）的进化提供了一个简单的实验范例。这种DNA分子的遗传成分和组织致力于维持其自身在群体中的稳定，而不会在细胞分裂时过度紧张质粒分子的代谢机制。一个同样由质粒编码的扩增系统，当质粒拷贝数由于偶尔的分区失败而下降时，将质粒拷贝数调整到正常水平。出于两个原因，放大系统必须精确地调节。首先，它必须在稳定的生长状态下被抑制，这样拷贝数的不受控制的增加就不会对宿主造成威胁，从而影响质粒的存活。其次，一旦副本数量下降，必须立即委托，以便副本数量在短时间内恢复到正常值。本项目试图从两个方面理解放大机制。首先，我们希望考虑可能的扩增模型，并通过使用适当设计的质粒底物来测试它们的预测。其次，我们希望分析由扩增系统的核心组件Flp重组酶介导的生化步骤在从单个复制起始事件产生多个质粒拷贝中是重要的。

The yeast plasmid 2 micron circle provides a simple experimental paradigm for the evolution of a selfish genome (or a benign molecular parasite). The genetic content and organization of this DNA molecule is devoted to maintaining itself stably in a population without unduly straining the metabolic machinery plasmid molecules at cell division. An amplification system, also encoded by the plasmid, adjusts plasmid copy number back to normal if and when it drops due to an occasional failure in partitioning. The amplification system must be exquisitely regulated for two reasons. First, it must be repressed under steady state growth, so that uncontrolled increase in copy number does not pose a threat to the host, and consequently to plasmid survival. Second, in the event of a fall in copy number, it must be commissioned immediately, so that copy number can be restored to the normal value within a short time. This project attempts to understand two aspects of the amplification mechanism. First, we wish to consider possible models for amplification, and test their predictions by using suitably designed plasmid substrates. Second we wish to analyze what biochemical steps mediated by the Flp recombinase, the central component of the amplification system, are important in the production of multiple plasmid copies from a single replication initiation event.