plasmid DNA prep using CsCl-EtBr

Frank Mullens frank.mullens at
Mon Jun 2 16:57:35 EST 1997

I have been troubled recently with my plasmid DNA prep using CsCl
gradient method. I have noticed that there were significant amount of
EtBr stuck to the DNA in some preparations (but not in all cases). EtBr
seemed bound to DNA very tight and tolerated repeat extraction using
1-butanol, even when I titrated pH to 10.00 in an attempt to neutralize
the positive group on EtBr. I wonder if these molecules somehow
covelently bound to the plasmid DNA. I am not certain how these residual
EtBr molecules may do to my experiment. Will they mess up my measurement
of DNA concentration? cause toxicity once being introduced to cells? Can
someone experienced offer me some hint on these questions and how to
avoid this problem? 


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