How to separate plasmid DNA from Chromosome DNA?

Stephen R. Lasky, Ph.D. Stephen_Lasky at
Tue Nov 29 14:45:08 EST 1994

In article <29NOV199411342814 at>, chee1tq at (Xu,
Liang) wrote:

> Is there any good way to separate chromosome DNA from plasmid DNA?
> Ony way I kown, is to use ultracentrifuge, since the molecular weights between
> plasmid DNA and chromosome DNA are different. But for the large scale
> plasmid DNA production up to couple hundred milogram, it is not a very
> good and efficent to use ultracentrifuge. Does anybody have good thought?

The standard alkaline lysis technique with KOAc precipitation does just
this if you are carefull to not shear the chromosomal DNA.  If you want to
use the centrifuge, you might want to try a CsCl gradient banding
technique that doesn't rely on size but on equilibrium density banding.
All you need is for your plasmid's boyant density to be different from the
chromosomal DNA boyant density.  


*********************************************************************Stephen R. Lasky, Ph.D.
Roger Williams Medical Center/Brown University
Phone: 401-456-6572       Fax: 401-456-6569       e-mail: Stephen_Lasky at
"To me at least, 'Yuck' doesn't capture the full essence of death by
neurotoxin."   -Dick Dunn

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