Hi All, We are refining several structures in which the N-terminal residue of chain A appears to form a peptide bond to the C-terminal residue of its symmetry mate, chain A. In reality, the target protein consists of 4 identical helical repeats that pack end to end. Slippage and averaging over the 4 possible registers leads to the appearance of an infinitely long polymer in the crystal, with no breaks between protomers. Is it possible to enforce a peptide bond to symmetry mates in Phenix, and what is the easiest way to do this? I have found a several cases in the archives on how to deal with symmetry clashes, but struggling to figure out how to deal with a peptide bond. Thanks for your help! Best, Damian - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Damian Ekiert Assistant Professor Skirball Institute | NYU School of Medicine Depts. Cell Biology and Microbiology [email protected] www.bhabhaekiertlab.org