Hi All, I am trying to see if I can save myself some time by using the loop fitting tools in Phenix. I think I am stalling out because of a trivial problem, but cursory googling, etc, has not helped. Sorry if I should have tried harder. I appreciate any help. I am using the gui, dev-601. My fasta sequence gets read fine because the output reports the sequence of the missing residues. Whether I use the loop library or not, I get the following error: Unable to find suitable gap to fill Then it appears to try to build the loop using sequence from a different chain (I have three chains in my structure). What am I doing wrong? Luke -- Luke M. Rice Assistant Professor and Thomas O. Hicks Scholar in Medical Research Department of Biochemistry, ND10.300 UT Southwestern Medical Center 5323 Harry Hines Blvd. Dallas, TX 75390-8816 phone: (214) 645-5931 email: [email protected]