Help:Plasmid backbones/Features

Copy Number

A plasmid's 'copy number' refers to how many times the plasmid self-replicates within a cell (via the origin of replication or [[1]]) and thus how many copies are present. This can play a significant role in intracellular systems, particularly BioBricked synthetic devices. Large DNA inserts can greatly reduce the copy number of a plasmid, despite the fact that they may originally be high-copy.

Most Biobricks are "high copy" type plasmids and are well-suited for high yield plasmid purification. These plasmids can reach large numbers by being replicated using host enzymes (source: [http://www.biochem.wisc.edu/courses/biochem651_f05/Lectures/08Plasmids/Theory_plasmids/copynumber.html University of Wisc. Madison])

Origin (of replication)

The origin of replication is a binding sequence where replication proteins which nick, unwind, and replicate plasmid DNA independently of the cellular host. Many biobrick plasmids have the following type of origin of replication:

• pmB1 - This origin has been isolated from one of the first plasmids taken from a human body. It is a "relaxed" plasmid, meaning that it allows high copy amounts within a cell

Note: This origin is not to be confused with the "origin of transfer", the site used in conjugal rolling circle replication transfer.

Size

The larger your plasmid is, the more difficult it will be for the cell to produce large quantities of it. Since the size of a plasmid can be determined by both the size of the bare plasmid backbone and the your construct inside of it. Thus it is generally a good idea to use plasmids of a small size.

Links and References

• [http://dwb.unl.edu/Teacher/NSF/C08/C08Links/mbclserver.rutgers.edu/~sofer/cloningvectors.html "Cloning Vectors and Genetic Engineering"] - from educators at Rutgers University
• [http://www1.qiagen.com/Plasmid/BacterialCultures.aspx?#tab2 "Plasmid Applications"] - Qiagen's guide