Rick Bright rbright at
Thu Dec 19 09:55:15 EST 1996

I have been using a protocol successfully to extract DNA from blood.  At
one point, I use a low salt buffer to salt in the proteins, coupled with
SDS.  I then add a high salt (5M NaCl) to precipitate the proteins and
follow with a spin to pellet them, leaving the DNA in the salt
solution.  As of yesterday, after this spin, it is not pelleting.  I
have the clear salt solution layer, but it is on the bottom of the tube,
while the "reddish" goo layer of the proteins is floating on top of the
salt solution.  How can this protein layer now have a lower density than
the salt/DNA solution?

1) Has my low salt buffer gone bad?  It was made on 11/18, consists of
TRIS/EDTA/0.4MNaCl, MgCl2, KCl.  It seems it would be stable for a long
while, I keep it refrigerated.

2) Has the SDS gone bad?  10%, I keep refrigerated and warm to rt before
use.  Does the cool, thaw cycle hurt it after a while, does it go bad
after a while?

I would appreciate any ideas.

rbright at

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