Helical Symmetry Axis

Hi All,

Is it possible to set up a symmetry definition file so that real atoms are locked into the same place as the virtual residues? I am trying to make a helical model for my protein using the symmetry module and for this model I need the same atom from each subunit to sit on the helical symmetry axis, around which the subunits rise and turn. I am attaching the symmetry definition file I have been using. This file does what I want with the virtual residues (in terms of twist and rise) and gives reasonable structures, but it often puts considerable distance between the virtual residues and the actual subunits. If I could make sure the same atom from each subunit was located on the corresponding virtual reside this would solve my problem. Does anyone know how/if this can be done?

Thanks,

Sandy