Figure 6. Structural similarities between AddB, Cas4 and a putative exonuclease DUF3799.

All three structures show the same arrangement of four cysteine residues forming a metal ligand, coupled with a RecB nuclease domain. However, unlike AddB (PDB: 3U44) and Cas4, DUF3799 (PDB: 3L0A) has a zinc ion (green sphere) coordinated with the cysteines instead of iron. The cartoons on the left show the conserved residues implicated in nuclease activity and FeS cluster binding.