As mentioned by the other poster, it may be easier just to buy a purer
preparation. Depending on your application, sonication will probably not
be the best solution, since you will likely end up shearing your DNA into
much smaller fragments.
If you really want to clean up the DNA you already have, you might
consider treating it like a viral DNA prep -- SDS + proteinase K treatment
followed by phenol and phenol/chloroform extractions, with a finishing
ethanol precipitation. (It wasn't clear from your post if you include
chloroform in your phenol extraction steps -- it makes the separation of
the layers much easier and helps to decrease sample loss.) The viral DNA
approach will take the better part of an afternoon, but should give nice
results.
--
______________________________________________________________________________
Lou Hom >K'93
lhom at ocf.berkeley.eduhttp://www.ocf.berkeley.edu/~lhom/
