Figure 2. Interaction between the N-termini of two CRX HD molecules bound to Ret4.

The N termini of the two CRX molecules come into close proximity. R41 in chain B is within hydrogen-bonding distance of E42 in chain A (2.6 Å). An omit map (Fo−Fc) for N terminal CRX residues (residue 41–43 of chain A and 39–43 of chain B) is contoured at 2.2σ and shown for 1.6 Å around the omitted residues (blue mesh). The omit map supports the interaction.