[phenixbb] DNA double helix with many molprobity bad clashes

[Benda, Christian]

Hi, 

I am refining a protein-DNA complex at around 3 A with a standard b-form dsDNA. R-factors are around 24/20 (kinda low for the resolution). Originally, I placed the DNA using coot and now, after several rounds of refinement in phenix, I get a long list of bad clashes from molprobity validation (in phenix) that covers the whole length of the DNA and almost exclusively lists hydrogens from the ribose moiety (whether or not in contact with protein). My question is, 

- why is phenix.refine not taking care of these clashes (i.e. optimizes the structure such that they go away)?. Am I giving experimental contribution to high a weight  (I have  "optimize x-ray/stereochemistry" checked)? 
- if so, can I (and how) restrain geometry for the DNA a little more but leave the protein alone (and does that make sense)?

thanks for any help

Christian