Replication and control of circular bacterial plasmids. An
essential feature of bacterial plasmids is their ability to
replicate as autonomous genetic elements in a controlled way
within the host. Therefore, they can be used to explore the
mechanisms involved in DNA replication and to analyze the
different strategies that couple DNA replication to other
critical events in the cell cycle. In this review, we focus on
replication and its control in circular plasmids. Plasmid
replication can be conveniently divided into three stages:
initiation, elongation, and termination. The inability of DNA
polymerases to initiate de novo replication makes necessary the
independent generation of a primer. This is solved, in circular
plasmids, by two main strategies: (i) opening of the strands
followed by RNA priming (theta and strand displacement
replication) or (ii) cleavage of one of the DNA strands to
generate a 3'-OH end (rolling-circle replication). Initiation is
catalyzed most frequently by one or a few plasmid-encoded