Plasmids, DNA (or rarely RNA) molecules which replicate in cells autonomously (independently of chromosomes) as non-essential genetic elements, play important roles for microbes grown under specific environmental conditions as well as in scientific laboratories and in biotechnology. For example, bacterial plasmids are excellent models in studies on regulation of DNA replication, and their derivatives are the most commonly used vectors in genetic engineering. Detailed mechanisms of replication initiation, which is the crucial process for efficient maintenance of plasmids in cells, have been elucidated for several plasmids. However, to understand plasmid biology, it is necessary to understand regulation of plasmid DNA replication in response to different environmental conditions in which host cells exist. Knowledge of such regulatory processes is also very important for those who use plasmids as expression vectors to produce large amounts of recombinant proteins. Variable conditions in large-scale fermentations must influence replication of plasmid DNA in cells, thus affecting the efficiency of recombinant gene expression significantly. Contrary to extensively investigated biochemistry of plasmid replication, molecular mechanisms of regulation of plasmid DNA replication in response to various environmental stress conditions are relatively poorly understood. There are, however, recently published studies that add significant data to our knowledge on relations between cellular stress responses and control of plasmid DNA replication. In this review we focus on plasmids derived from bacteriophage lambda that are among the best investigated replicons. Nevertheless, recent results of studies on other plasmids are also discussed shortly.

中文翻译：

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应激反应和细菌细胞中质粒的复制。

质粒，DNA（或很少有RNA）分子作为非必需的遗传元件在细胞中自主复制（独立于染色体），对在特定环境条件下以及科学实验室和生物技术中生长的微生物起着重要作用。例如，细菌质粒是DNA复制调控研究中的优秀模型，它们的衍生物是基因工程中最常用的载体。对于几种质粒已经阐明了复制起始的详细机制，这是在细胞中有效维持质粒的关键过程。但是，要了解质粒生物学，有必要了解响应宿主细胞存在的不同环境条件而对质粒DNA复制的调控。对于那些使用质粒作为表达载体来产生大量重组蛋白的人来说，此类调节过程的知识也非常重要。大规模发酵中的可变条件必须影响质粒DNA在细胞中的复制，从而显着影响重组基因表达的效率。与广泛研究的质粒复制的生物化学相反，响应各种环境胁迫条件调节质粒DNA复制的分子机制相对了解得很少。但是，最近发表的研究为有关细胞应激反应和质粒DNA复制控制之间关系的知识增加了重要的数据。在这篇综述中，我们关注于噬菌体λ衍生的质粒，它们是研究最好的复制子之一。