Desalting of Plasmid DNA after Cesium Preps

Frank O. Fackelmayer fof1 at
Thu Jul 9 10:24:22 EST 1998

Chris Boyd wrote:

> I think you always lose a lot doing ethanol precipitation, particularly
> in the washing stage which is necessary to remove salt traces.
> You have to make a choice: time or yield + quality.

I disagree. Some years back we did a parallel test to see what is better,
direct EtOH precipitation after dilution (see my first posting for the
method), or dialysis. Result: yield with direct precip was *TWICE* that of the
dialysed sample (3mg compared to 1.6mg). In addition, direct precip was
finished in 2h, while dialysis took 5h plus overnight plus EtOH precip (1h).
That´s 2:16, factor 8 in speed. Not bad for a method with twice the yield. I
have to add that we did not see ANY difference in DNA quality (restriction
digests, sequencing, transfection were all exactly the same). So, slower is
not always better.

BTW, I enjoy this thread, as it shows there are still other people out there
who prefer good old CsCl over the kits used in almost all labs. Its simply
better, that´s why.

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