Initiation of Replication of Plasmid ColE1 DNA by RNA Polymerase, Ribonuclease H, and DNA Polymerase I

Colicin E1 (ColE1) plasmid is an Escherichia coli plasmid of approximately 6600 bp (H. Ohmori and J. Tomizawa, in prep.). The plasmid DNA can be replicated in vitro by a soluble enzyme system (Sakakibara and Tomizawa 1974a; Tomizawa 1977). This replication proceeds through a unique class of early replicative intermediates containing newly synthesized 6S DNA fragments (Sakakibara and Tomizawa 1974b). The 6S L-strand fragment, which hybridizes to the H-strand DNA of ColE1, is synthesized first (Tomizawa 1975). Synthesis of the 6S L-strand DNA is initiated at any of three consecutive nucleotides located at a unique position (Tomizawa et al. 1977). Further replication proceeds by unidirectional expansion of the replication loop of this early replicative intermediate (Tomizawa et al. 1974; Tomizawa 1975). Usually DNA synthesis of the leading strand is followed by that of the lagging strand (Tomizawa et al. 1974; Tomizawa 1977). Both strands of ColE1 DNA seem to be...