I have an EM map for a virus that includes an antibody bound to the envelope proteins.  The envelope proteins are trimers of dimers with C3 symmetry that form spikes on the surface of the virus.   I fit an atomic model for the spikes to the map using icosahedral symmetry, following the very helpful symmetric fitting video tutorial.  Now I am trying to fit a model for the antibody into the spike regions of the map.  I need to impose C3 symmetry for the antibody for the fit into each spike, in addition to imposing icosahedral symmetry to include all the spikes.  How can I impose both of these in the fit?  

Thanks,

​Mike Kent