Colicin E9 from Escherichia coli is a non-specific endonuclease. This extracellular toxin is secreted by strains of Escherichia coli to kill competing bacteria. It kills the cell by enzymatic cleavage of nucleic acids once it has entered the cell. Since colicin E9 is non-specific, it can hydrolyse both single and double stranded DNA.
Defined by 7 residues: ARG:B-5ARG:B-96GLU:B-100HIS:B-102HIS:B-103HIS:B-127HIS:B-131