Plasmid extraction

the End jgraham at bronze.ucs.indiana.edu
Tue Mar 8 12:56:04 EST 1994


Joanne,

One tip to AVOID in preparation of large plasmids is one that suggests 
freezing your bacterial pellet prior to lysis. The authors claim that it
increases recovery of low copy plasmids.

In my expereince this step does little to increase yield, and has a 
substantial effect on increasing chromosomal contamination of plasmid
DNA. Presumably the association of the bacterial chromosome with the 
membrane and associated proteins in the subsequent percipitate is reduced.

I have seen this with plasmids in the 10-15 Kb range. If you intend to 
CsCl purify larger plasmids, then perhaps a potential benefit could outweigh
this problem.

Jim



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