title: Mechanisms of Theta Plasmid Replication.
abstract: Plasmids are autonomously replicating pieces of DNA. This chapter discusses theta plasmid replication, which is class of circular plasmid replication that includes ColE1-like origins of replication popular with expression vectors. All modalities of theta plasmid replication initiate synthesis with the leading-strand at a pre-determined site and complete replication through recruitment of the host's replisome, which extends the leading-strand continuously while synthesizing the lagging-strand discontinuously. There are clear differences between different modalities of theta plasmid replication in mechanisms of DNA duplex melting and in priming of leading- and lagging-strand synthesis. In some replicons duplex melting depends on transcription, while other replicons rely on plasmid-encodedtrans-acting proteins (Reps); primers for leading-strand synthesis can be generated through processing of a transcript or in other replicons by the action of host- or plasmid-encoded primases. None of these processes require DNA breaks. The frequency of replication initiation is tightly regulated to facilitate establishment in permissive hosts and to achieve a steady state. The last section of the chapter reviews how plasmid copy number is sensed and how this feedback modulates the frequency of replication.
authors.affiliation: Department of Microbiology and Environmental Toxicology, UC Santa Cruz, 1156 High Street, Santa Cruz, CA 95064.
authors.forename: Joshua
authors.initials: J
authors.lastname: Lilly
authors.affiliation: Department of Microbiology and Environmental Toxicology, UC Santa Cruz, 1156 High Street, Santa Cruz, CA 95064.
authors.forename: Manel
authors.initials: M
authors.lastname: Camps