C-terminal domain structure of Ca FADS. (A) Comparison of the structural elements with those found in RFKs. (B) Model for the interaction of ADP-Mg2+ and RF with the C-terminal domain. Residues putatively involved at the RFK active site, nucleotides and flavins are shown in CPK sticks. Carbon atoms are shown in green, white and orange for protein side-chains, nucleotides and RF, respectively. Mg2+ ions are shown as yellow balls.