From: Jack Correia <jcorreia@fiona.umsmed.edu>
  To  : rasmb@bbri.eri.harvard.edu
  Date: Wed, 8 Mar 95 10:27:02 -0600

Re: Surfactant + DNA

        Upon returning to the USA and Miss. from Berlin (a great meeting and 
experience) I found my XLA spinning with a sonicated DNA sample (~200 bp) + 
a surfactant, dodecyltrimethylammoniumbromide.  Alex, my tech, and Charlie 
Spink, on sabbatical from SUNY Cortland, where looking at the size of the 
micelle/DNA complex.  The DNA, 0.4 OD at 260 nm, alone has an S value of ~6. 
 To our surprize the mixture at 6 mM or 25 mM surfactant had no absorbance 
at 260 nm.  We monitored at 218 nm and saw no sedimentation.  There were no 
obvious boundaries, flotation or otherwise.  Upon stopping the run we 
checked the samples by UV in a Cary 60 and the 260 nm signal was back????   
Thus spinning (pressure?) had caused a suppression of signal that was 
reversible.  A phase change, surface separation?, that caused the complex to 
be out of sight of the optics is our hypothesis.  (Where it actual goes is 
the question?)

  Any experience with this in the XLA model E world??  Suggestions?

jack correia