Cross-linking maps of BpeGReg and PccGCS tetramer forms. (A) Cross-links for BpeGReg. (B) Cross-links for PccGCS. The three domains of the proteins are shown with the arrangement of their secondary structures (drawn approximately to scale). Lysine residues are shown as red lines within the domains and numbering is based on native residue numbering. Cross-links were identified using Spectrum Identification Machine [29,30].