REPLICATION ASSOCIATED GENETIC REARRANGEMENTS

描述：两种大肠杆菌中缺失突变的序列分析。杆菌和 人类已经表明，缺失最频繁地发生在短 重复的序列。 解释这一现象的模型有两种 主要类型：重组（不等交换）和复制 （股线滑动或未对准）。 有一种趋势， 由于E.杆菌 缺乏同源重组的两个传统标志： 序列通常比作为一个 RecA蛋白的底物，并且缺失很容易在 RecA缺失菌株，其中常规重组是 淘汰 洛维特博士最近的工作是使用基于质粒的系统， 监测缺失显示，出乎意料的是， 缺失形成可以具有明确的重组特征， 值得注意的是缺失相关的质粒二聚化。 在此基础上 和相关的观察，洛维特博士提出了一个机制， 缺失形成起始于RecA-独立配对新生 链在附近的一个被捕的复制叉，以形成一个 假期结，其次是处理由其他酶相关联 同源重组反应。 洛维特博士还说 建议同样的机制可能适用于重组 在受损的DNA模板上观察到“复制后”修复， 机制一直模糊。 在这份申请中，洛维特博士建议继续她的研究， 缺失形成机制及其与重组的关系 DNA修复和姐妹链交换（质粒二聚化）。杆菌 拟议的工作有两大组成部分。 在一个组件，博士。 洛维特将分析单个DNA损伤（胸腺嘧啶二聚体）的影响。 对缺失和质粒二聚化的发生的影响。 她将研究胸腺嘧啶二聚体是否具有不同的 当放置在领先与落后链与两者一起时的效果; 当被放置在相对于串联重复的 重组的序列;当在菌株中处理时， 重组或复制的各种成分中的突变。 在 在调查的另一部分，洛维特博士将确定遗传学的 recA非依赖性缺失形成通过检查已知的 缺失形成时的复制和重组组分，以及 通过寻找影响基因缺失频率的新基因 阵

DESCRIPTION: Sequence analysis of deletion mutations in both E. coli and humans has shown that deletions occur most frequently between short repeated sequences. Models to explain this observation have been of two main types: recombinational (unequal crossing over) and replicational (strand slippage or misalignment). There has been a tendency to discount recombinational mechanisms because deletion mutations in E. coli lack two traditional hallmarks of homologous recombination: the repeated sequences are very often much shorter than necessary to serve as a substrate for RecA protein, and the deletions occur quite readily in RecA deletion strains, in which conventional recombination is eliminated. Recent work by Dr. Lovett using a plasmid-based system for monitoring deletions has shown, unexpectedly, that RecA-independent deletion formation can have unmistakable recombinational features, most notably, deletion-associated plasmid dimerization. On the basis of this and related observations, Dr. Lovett has proposed a mechanism for deletion formation initiated by RecA-independent pairing between nascent strands in the vicinity of an arrested replication fork to form a Holiday junction, followed by processing by other enzymes associated with homologous recombination reactions. Dr. Lovett furthermore proposes that the same mechanism may apply to recombinational "postreplication" repair observed on damaged DNA templates, whose mechanism has been obscure. In this application, Dr. Lovett proposes to continue her study on the mechanism of deletion formation and its relationship to recombinational DNA repair and sister strand exchange (plasmid dimerization) in E. coli. The proposed work has two broad components. In one component, Dr. Lovett will analyze the effect of single DNA lesions (thymine dimers) on the occurrence of deletions and plasmid dimerization.Using variations of this basic idea, she will examine if a thymine dimer has different effects when placed in the leading vs. lagging strand vs. both together; when placed in different locations relative to the tandemly repeated sequences that are recombining; and when processed in strains with mutations in various components of recombination or replication. In the other part of the investigation, Dr. Lovett will define the genetics of recA-independent deletion formation by examining the effects of known components of replication and recombination on deletion formation, and by searching for novel genes that affect the frequency of deletion formation.