The plasmid copy number and plasmid respectively DNA concentration are 2 different pair of shoes. The copy number of a plasmid is depending on the origin of replication (ORI) they contain. The different ORIs regulate the replication mechanism of the plasmid. High-copy plasmids often contain mutated versions of an ORI. This link provides you an overview of some plasmid that are used and their copy numbers http://www.qiagen.com/plasmid/bacterialcultures.aspx. I hope this helps you.

Plasmid concentration. You have enough concentration. OD260 have above 0.5, because it has to time 40ug/mi.

The plasmid copy number and plasmid respectively DNA concentration are 2 different pair of shoes. The copy number of a plasmid is depending on the origin of replication (ORI) they contain. The different ORIs regulate the replication mechanism of the plasmid. High-copy plasmids often contain mutated versions of an ORI. This link provides you an overview of some plasmid that are used and their copy numbers http://www.qiagen.com/plasmid/bacterialcultures.aspx. I hope this helps you.

The reason is when the plasmid replicated in bacteria, it is also partly controlled by bacteria chromosome, if this contol is loose, then high copy number, if it is stringent, then low copy number.

Gang Zhang University of Toronto

The bacteria itself is not regulating if the plasmid is a high copy or a low copy plasmid. It is just regulated and determined by the plasmid itself and the encoded origin of replication as Thomas already explained.

the ori of your plasmid controls the number of plasmid copies in the bacteria, for example in E. coli: if you choose a plasmid with the ori pBR322 (pUC18, pBSKS, pET system) you will have 20-30 copies/bacteria, but if you choose a plasmid with p15A ori (pLEX) then you will have only 3-5 copies per bacteria.

There is a concept called antisense RNA control of plasmid copy number. Kindly read that. In breif, RNA ii is the primer that starts the plasmid replication. But, RNAi is an antisense RNA to RNAii that binds to RNAii and ROP (Repressor of primer) protein stabilizes this RNAi-RNAii complex. some plasmids have a mutation in RNAi sequence or lack of ROP protein thus preventing the RNAi-RNAii complex formation. hence these plasmids will be in high copy number. First of its kind is developed in University of California (UC) and the plasmids are named pUC.

Hello, I have another question around this topic, Is it possible not to be able to amplify sequences carried by low-copy plasmids  py classic PCR? Thanks in advance.

That depends on amount of the DNA and interfering compounds, how well your primers work and how many cycles of PCR you do.

In principle, you should be able o deec single copy of DNA. In practice, you do not have to get signal.