[ccp4bb] Mysterious density

[Nick Quade]

Dear CCP4 community,

I have solved the structure of a protein in complex with DNA. But, 
inside the protein there seems to be a ligand binding pocket with some 
strong density 
(*http://picasaweb.google.de/113264696790316881054/Desktop#). *The 
protein was in Tris buffer, with some NaCl, MgCl2 and DTT and 
crystallized in Li2SO4 with MES. What could this density be? I can 
exclude MES as crystals grown with citrate buffer have the same density. 
So I guess it might be something I co-purified or perhaps some 
degradation product of the DNA? The electron density in the pictures is 
at 1.5sigma.

Thanks in advance.

Nick