Copy number control of the yeast plasmid

酵母质粒2微米圈为自私基因组(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分子的遗传内容和组织致力于在一个群体中保持自身的稳定，而不会在细胞分裂时过度拖累新陈代谢机制的质粒分子。同样由该质粒编码的扩增系统，在由于偶尔的分割失败而使其下降时，将其调整回正常的拷贝数。出于两个原因，必须对扩增系统进行严格的监管。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才不会对宿主构成威胁，从而不会威胁到质粒的生存。第二，在副本数量下降的情况下，必须立即启用，以便在短时间内将副本数量恢复到正常值。这个项目试图从两个方面来理解放大机制。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检验它们的预测。其次，我们希望分析由FLP重组酶(扩增系统的中心组件)介导的哪些生化步骤在从单个复制起始事件产生多个质粒拷贝的过程中起重要作用。

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.