intermediate is characteristic of rolling-circle replication and its identification provides evidence that a plasmid replicates by this mechanism (48). The lagging-strand origin (also known as the single-strand origin) is exposed on the displaced single-stranded inter­mediate and lagging-strand initiation commences at this origin using host replication factors. RNA polymerase synthesizes RNA primers at the lagging strand origin. DNA polymerase I initiates lagging strand synthesis from these RNA primers, after which DNA polymerase III continues elongation.