The following plasmid DNA was prepared in low nuclease host bacteria and isolated through ion exchange chromatography. It is available in supercoiled form (ccc-form >95%) and, as a high-purity DNA (OD_260/280 > 1,70), it is ideal for different applications:

The circular sequence was numbered in such a way that 0 lies in the middle of the singular EcoR l restriction site. The copy number of pBR322 is limited by the gene product of rop to 20 copies per cell. However, by adding chloroamphenicol (final concentration 170 µg/ml) to log-phase cultures and then incubating for 8 hours, the copy number can be increased considerably.