The origin of replication of plasmid p15A and comparative studies on the nucleotide sequences around the origin of related plasmids.

Replication of Escherichia coli plasmid p15A was examined by use of a cell extract or a mixture of three purified E. coli enzymes: RNA polymerase; RNAase H; and DNA polymerase I. In each system, replication initiates at any of three consecutive nucleotides located at a unique site. Primer transcription starts 508 bp upstream of the replication origin. The region between 294 and 524 bp upstream of the origin determines the incompatibility property. This region specifies an RNA (RNA I) of about 105 nucleotides that is involved in regulation of primer formation. We compare the nucleotide sequences around the origins of related plasmids p15A, ColE1, pBR322, RSF1030 and CloDF13, and discuss the significance of possible RNA secondary structures in primer formation.