Stable maintenance of an extrachromosomal selfish DNA

描述（由申请人提供）：酵母质粒2微米圈提供 一个简单的模型系统，以研究分子机制， 寄生虫基因组“优化其生存策略，而不损害 它的主人的健康。质粒的信息内容和组织 基因组的设计是为了使其在种群中稳定地维持在一个稳定的水平上。 说明不使宿主代谢机制紧张的拷贝数。一 这种高拷贝自我繁殖机制的分子组成部分是一种稳定性 确保复制质粒分子均匀分布的系统， 细胞分裂过程中的子细胞两个质粒编码的蛋白质， 与顺式作用的DNA序列（称为STB基因座），是必不可少的 稳定系统的正常运行。此外，宿主编码因子可 有助于质粒的均分。这个2微米的圆圈也 设计了一个放大系统，只有当有 由于偶而未能均等分离而导致拷贝数下降。 扩增由Flp重组酶（Flp用于翻转或反转）介导 DNA），其活性将单个复制起始事件转化为 多重复制机制，从而快速恢复副本数量。 在这个提议中，我们描述了一些实验，试图阐明 质粒和宿主编码的组分相互作用， 稳定系统我们相信从中得到的一些原则 这项研究将在全球范围内对以下方面的共生关系产生影响 原核生物和真核生物中的宿主-寄生虫基因组。

DESCRIPTION (provided by applicant): The yeast plasmid 2 micron circle provides a simple model system to study the molecular mechanisms by which a 'benign parasite genome' optimizes its survival strategies without compromising the fitness of its host. The informational content and organization of the plasmid genome is designed for its stable maintenance in the population at a steady state copy number that does not strain the host metabolic machinery. One molecular component of this high copy self-propagation mechanism is a stability system that ensures equal distribution of replicated plasmid molecules to daughter cells during cell division. Two plasmid-encoded proteins, together with a cis-acting DNA sequence (called the STB locus), are essential for the normal operation of the stability system. In addition, host encoded factors may contribute towards equipartitioning of plasmids. The 2-micron circle has also devised an amplification system, which comes into operation only when there is a drop in copy number due to an occasional failure in equal segregation. Amplification is mediated by the Flp recombinase (Flp for flipping or inverting DNA), whose activity converts a single replication initiation event into a multiple copying mechanism, thus quickly restoring copy number. In this proposal, we describe experiments that attempt to shed light on how the plasmid and host encoded components interact to establish a functional stability system. We believe that some of the principles gleaned from this study will have global implications in the symbiotic relationships among host-parasite genomes in prokaryotes and eukaryotes.