If a plasmid has too high of a copy number, they may excessively burden their host by occupying too much cellular machinery and using too much energy.
The partitioning system interacts with the septation apparatus to ensure that each daughter receives a copy of the plasmid.
Larger high copy plasmids (>30kb) are disfavoured and also prone to size reduction through deletional mutagenesis.
Relaxed plasmids are generally regulated through one of two mechanisms: antisense RNA or iteron binding groups.
RNA I serves as a major plasmid-encoded inhibitor of this process whose concentration is proportional to plasmid copy number.
The kissing complex is stabilized by a protein called Rop (repressor of primer) and a double-stranded RNA-I/RNA-II RNA duplex is formed.
This altered shape prevents RNA II from hybridizing to the DNA and being processed from RNaseH to produce the primer necessary for initiation of plasmid replication.
The synthesis of Rep protein is controlled in order to limit plasmid replication and therefore regulate copy number.
[3] RepA expression is also regulated post-transcriptionally from the secondary promoter by an antisense RNA called CopA.
CopA interacts with its RNA target in the RepA mRNA and forms a kissing complex and then a RNA-RNA duplex.