Plasmid DNA Replication

Abstract Plasmids are extrachromosomal replicons found in gram‐negative and gram‐positive bacteria as well as in some lower eukaryotic organisms. They are present in bacterial cells replicating at a specific number of copies per cell. Their size varies from a few to several hundred kilobase pairs and bacterial cells can harbor more than one plasmid species. The medical importance of plasmids that code for antibiotic resistance and those that contribute directly to microbial pathogenicity is well‐documented, is the role played by plasmids in bacteria of importance in agriculture and industry. These extrachromosomal elements are of equal importance, however, for the study of the structure and function of DNA. Plasmids utilize a wide variety of strategies to initiate and regulate their replication. In this chapter we examine the replication of plasmids ColE1, whose replication system is part of most plasmids vectors; R6K, an iteron‐containing plasmid that possesses three replica origins; plasmids belonging to the RepABC family found in a‐proteobacteria; and of pT181, a group of plasmids found in gram‐positive bacteria. In addition,we also discuss linear plasmids.