Figure 8.

The conserved and non-conserved molecular surface of nuclease-ColE7. The molecular surface that contains the conserved residues in the six bacteria toxins in HNH family is colored red, and the non-conserved surface is colored white. Im7 is displayed in a ribbon model in blue. The protein interface is not conserved, therefore the immunity protein specifically recognizes its cognate colicin. On the contrary, the zinc ion is located in the middle of a conserved surface where it is likely that the DNA-binding site and DNase-active site are located.