PROTEIN CRYSTAL or SALT CRYSTAL??!

[WILLARD at MVAX.WISTAR.UPENN.EDU]

Dear fellow crystallographers:

I have been trying to crystallize a zinc finger protein in complex with its
DNA binding site (a 20 mer oligodeoxynucleotide).  Well, on monday I looked
at one of my trays in which I had set up a factorial screen and low and 
behold, I saw a beautiful, single, multi-faceted (kind of cubic-looking)
0.2 mm/edge crystal.  However, since we share an area detector, I cannot
look at diffraction until this monday.

The complex (8 mg/ml DNA; 6.5 mg/ml protein) was in 350 mM MgCl2 before I
mixed it 1:1 with the well solution (0.1 M Tris pH 8.5; 2.0 M (NH4)2PO4).

My question is, do you think it is most likely protein, or is such a c          
combination of magnesium and phosphate likely to form a beautiful 
Mg Phosphate crystal??!!

At any rate, we'll know on monday.  Any insight would be appreciated.

Thanks.

Rob Willard
University of Pennsylvania
Dept. of Chemistry/The Wistar Institute