You should add some salt when you anneal!!! The duplex is highly negatively charged, so adding even a small amount (like 10mM NaCl) will help with charge screening, thus making the two strands less repellant to each other. Buffer is also always a good idea. At low pH and high temp you'll hydrolyze the glycosidic bonds of your purines. Also, depending on how you purified the DNA after synthesis, the white precipitate may well be other crud - protecting groups, etc. Did you desalt it at least? DNA should be very highly soluble, so your complex protocol should depend mostly on the protein's personality. If it is also highly soluble, just mix them. Finally, if you try crystallization with each possible duplex one at a time, you'll be a post-doc for a very long time. We usually try at least a half-dozen at a time (with varying ends), and it usually takes several different crystal forms to get one that diffracts decently. Good luck! Phoebe Phoebe A. Rice Assoc. Prof., Dept. of Biochemistry & Molecular Biology The University of Chicago phone 773 834 1723 http://bmb.bsd.uchicago.edu/Faculty_and_Research/01_Faculty/01_Faculty_Alphabetically.php?faculty_id=123
RNA is really nifty DNA is over fifty We have put them both in one book Please do take a really good look http://www.rsc.org/shop/books/2008/9780854042722.asp
