Abstract
Pulse-labeled colicin E1 plasmid (Col E1) DNA in minicells was examined to characterize replicating molecules. Replication of Col E1 DNA principally occurred in covalently closed molecules and involved the synthesis of variable length single-stranded DNA fragments that were dissociable from the template DNA and ultimately incorporated into the completely replicated molecules. RNA was found to be associated with some of these newly synthesized fragments. Replicating molecules containing different size displacement loops were observed by electron microscopy.