I have a question about the proper procedure for building homomers. My test case is a trimeric coiled-coil with 3-fold symmetry (trimer in assymetric unit). My input model is a trimer with three chains (A,B,C) with identical sequence. If I run phenix autobuild (rebuild_in_place=False) with this model I get a structure with decent R/Rfree. However, there are some issues: 1) Helix 1 consists of chain A in the output structure. There is a jump in the sequence number for chain A at the end. However, disregarding this chain break the full sequence is correct for helix 1. 2) Helix 2 consists of chain B + C in the output structure. The chain B has the correct sequence for helix 2. Chain C has partly the right sequence for helix 2. 3) Helix 3 consists of chain C in the output structure. Chain C has partly the correct sequence for helix 3. Lots jumps in the sequence numbering. GIven that I know its has three subunits with identical sequences I gather it should be possible to have autobuild generate structures with three chains with identical sequences. I have tested a few things. With and without giving it the sequence file corresponding to the sequence of a monomer. With and without enforcing ncs based on the input model (find_ncs=False input_ncs_file=find_ncs.ncs_spec). I am never able to build sequence-symmetric structures with rebuild_in_place=False for any homomer I have tried to build. I have limited experience with phenix so it is likely I am missing something obvious. In any case, I would appreciate your input on this. Best regards, Ingemar