Dear Zhe, I think Phenix can handle it without the need of specifying whether it will be A or B. These might be too "strong" constrains in a way from my point of view. Your DNA may be mostly B if it is unmodified, with the exception of some part of the helix that has some C3´-endo puckers and therefore there "it would be A", say. By default the nucleic acids restraints are on, I would just keep working and refining, safest way to go indeed is to place the phosphates where they should be, Phenix will take care of assigning the puckers. If you want to compare your dsDNA with an ideal A type of helix DNA or B type of helix DNA, you can just build yourself some withing coot. You find this option under calculate/other modelling tools/ideal RNA/DNA. I hope this helps, Best wishes, Almudena 2016-02-23 4:50 GMT+01:00 Zhe Li :

I am refining a protein-dsDNA complex structures at 2.4-3 A. Based on the phosphate distance, I can predict if particular nucleotide is A DNA (C3’-endo) or B DNA (C2’-endo). I want to add restrain to to the specific nucleotides as A or B DNA. But secondary_structure_restraints for nucleic acid does not seem to have options for this. Any suggestions? Thanks _______________________________________________ phenixbb mailing list [email protected] http://phenix-online.org/mailman/listinfo/phenixbb Unsubscribe: [email protected]

-- Almudena Ponce-Salvatierra Macromolecular crystallography and Nucleic acid chemistry Max Planck Institute for Biophysical Chemistry Am Fassberg 11 37077 Göttingen Germany