I have another related question: If I were to deposit a PDB coordinates file of a helical structure, what would be the best place to put helical symmetry information (the file includes the full coordinates for only one asymmetric unit) so that chimera can generate a model with more than one asymmetric unit ?. The idea being to be able to see the contacts between asymmetric units and the symmetry of the complex. Should I use the the SMTRY, or the MTRIX entries ?. Does it make any difference in chimera ?. Thanks Hernando . -- ----------------------------------- Hernando Sosa Dept. of Physiology and Biophysics Albert Einstein College of Medicine 1300 Morris Park Av. Bronx NY 10461 phone (718) 430-3456 FAX (718) 430-8819 email hsosa@aecom.yu.edu -----------------------------------