Rolling-Circle Replication

Abstract

Plasmids that replicate by a rolling-circle (RC) mechanism are ubiquitous in gram-positive bacteria and are also found in gram-negative bacteria as well as in Archaea. This chapter discusses the general anatomy of rolling-circle replicating (RCR) plasmids, architecture of the double-strand origin (dso), the single-strand origin (sso), the initiator proteins and their structure-function relationship, key events during the initiation and termination process, and the role of host proteins in plasmid RC replication. It highlights the gaps in the current understanding of the replication of RCR plasmids and possible future lines of research that may uncover these gaps. The first of the RCR plasmids to be identified were native to the gram-positive bacterium, Staphylococcus aureus. The Rep proteins of the pT181 family act as dimers and utilize Tyr-191 of the two monomers in the initiation and termination events. Biochemical analyses using heterodimers of the pT181 RepC protein have provided insights into the role of individual monomers in plasmid RC replication. Elucidation of the three-dimensional structure of plasmid Rep proteins should considerably increase the understanding of the mechanistic aspects of plasmid RC replication. The availability of crystal structures of the initiators of various plasmid families should provide major insights into the mechanisms of initiation and termination of plasmid RC replication.