Glycine repeat-mediated interaction between two helices in E. coli site-specific recombinase. The helix-helix interaction in E. coli site-specific recombinase (PDB ID 1HJR) is shown. (A) A side view of the helices that undergo glycine repeat-facilitated dimerization. The pink squares represent the atoms of the residues in the glycine repeat segment. (B) An end-on view of the same interaction. (C) A more detailed representation of the interactions of the individual residues in the glycine repeat, viewed from the side. (D) Detailed representation viewed end-on. (A) and (B) were produced using PyMol , while (C) and (D) were produced using TURBO-FRODO .