Asymmetric replication of an oriC plasmid in Escherichia coli |
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Authors: | Makoto Yoshimoto Kazuo Nagai Gakuzo Tamura |
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Affiliation: | (1) Department of Agricultural Chemistry, The University of Tokyo, Bunkyo-ku, 113 Tokyo, Japan;(2) Present address: Research Laboratories of Taisho Pharmaceutical Co., Ltd., 330 Omiya Saitama, Japan;(3) Present address: Department of Applied Biological Science, Science University of Tokyo, 278 Noda, Chiba, Japan |
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Abstract: | Summary Plasmid pTSO118 containing the Escherichia coli origin of replication, oriC, initiated replication simultaneously with the chromosome when temperature-sensitive host cells were synchronized by temperature shifts. Replicating intermediates of the plasmid as well as of the chromosome were isolated from the outer membrane fraction of the cell. Plasmid DNA with eye structures was enriched when cytosine-1- -arabinofuranoside was introduced into the culture during replication. Electron microscopy of the replicating molecules, after digestion with restriction endonucleases, showed that the replication fork proceeds exclusively counter-clockwise towards the unc operon. We conclude that the replication of the oriC plasmid is unidirectional or, if bidirectional, is highly asymmetric. |
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Keywords: | Escherichia coli Replication OriC plasmid Membrane Electron micrograph |
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