Dear all,

I am trying to do a phenix.real_space_refine in a CryoEM map at 4.2 Å with a model obtained by MDFF (NAMD, a protein DNA complex) because the resulting structure, despite a good CC and a good molecular geometry has a poor Ramachandran Map.

When doing the phenix.real_space_refine, the CC is slightly increased with respect to the starting structure, the Ramachandran is dramatically increased but some part of the model ( in the case, the first three bases pairs a DNA duplex) are strongly distorted because of a lack of density in the corresponding region of the map.

For some reason, this does not append with the MDFF method.

I was wondering if there is a mean, in phenix.real_space_refine, to exclude a part of the model from being fitted in the map. Indeed, the distortion I observe in the DNA duplex is likely due to the fact that the real_space_refine tries to put the atoms at the extremity of the duplex in the closest density at the price of a strong distortion of the structure.

Thank in advance for your suggestions.

Best regards.

Philippe.

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Philippe Cuniasse, PhD/HDR.

Institut de Biologie Integrative de la cellule.

UMR 9198 CNRS-CEA-Univ Paris Sud

Bat 144 CE-Saclay

91191 Gif-sur-Yvette Cedex

France

Tel:      (33) 1 69 08 56 35

Fax:      (33) 1 69 08 47 12

Email: [email protected]

Web: http://biodev.cea.fr/rasmot3d/

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