The icon is a depiction of repressor-operator-effector cocrystals for the methionine biosynthesis regulon repressor (metJ) (left) and the tryptophan biosynthesis repressor (trpR).
DNA recognition peptides are colored in cyan: alpha helices for trpR on the left and beta ribbons for metJ on the right. Allosteric ligands (Tryptophan and S-adenosyl methionine respectively) are in yellow. The two strands of DNA in shades of red.
The image was prepared using RasMol, based on the PDB entries 1TRR (trpR) and 1CMA (metJ)