CsCl/EtBr preps - Strange Band!

Martin Kennedy mkennedy at
Thu Nov 18 20:42:29 EST 1993

In article <9311171934.AA29765 at>, tupy at ("Tupy.Jon") writes:
> I have a question for all of you who still indulge in the toxic messiness of
> CsCl/EtBr density gradient plasmid preps: from time to time people in this lab have
> been discovering an annomolous *white* band that seems to migrate just below (if
> they're lucky) the banded plasmid.  Sometimes, for the unfortunate, it occupies
> the same spot on the gradient as the desired DNA.  

> Jon Tupy

We used to see this sort of crud in our preps frequently (though I've avoided
cesium preps now for several years); it seemed to be an insoluble aggregate of
something with ethidium bromide.  I used to add the ethidium before adding
cesium, let the preps sit for an hour or so and spin it out.  As I recall it
pellets ok, but once the cesium is present you'll never get rid of it. This
helped, but I don't think it completely cured the problem


NNNN   NN  Martin A Kennedy (E-mail = mkennedy at  ZZZZZZZ  
NN NN  NN       Cytogenetic and Molecular Oncology Unit          ZZZ
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