Control of plasmid replication and copy-number

The copy-number of a plasmid in the cell is determined by regulating the initiation of plasmid replication. The initiation of plasmid replication may be controlled by regulating the amount of available primer for the initiation of DNA replication, regulating the amount of essential replication proteins, or regulating the function of essential replication proteins. Two major mechanisms are used to control the initiation of plasmid replication:

  1. Regulation by antisense RNA;
  2. Regulation by binding of replication proteins to repeated 18-22 bp sites called iterons.
A few examples of each type of regulation are shown in the figures below. Note that there are examples of high copy-number plasmids and low copy-number plasmids that use each mechanism.

Regulation of plasmid colE1 copy number by antisense RNA:

Regulation of plasmid R1 copy number by antisense RNA:

Regulation of plasmid copy number by iterons:


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Last modified October 18, 2004