Termination of DNA replication of bacterial and plasmid chromosomes

Sequence‐specific replication termini occur in many bacterial and plasmid chromosomes and consist of two components: a cis‐acting ter site and a trans‐acting replication terminator protein. The interaction of a terminator protein with the ter site creates a protein–DNA complex that arrests replication forks in a polar fashion by antagonizing the action of the replicative helicase (thereby exhibiting a contrahelicase activity). Terminator proteins also arrest RNA polymerases in a polar fashion. Passage of an RNA transcript through a terminus from the non‐blocking direction abrogates replication termination function, a mechanism that is likely to be used in conditional termini or replication check points.