Endonuclease I is a periplasmic or extracellular enzyme present in many different Proteobacteria. TheendAgene encoding endonuclease I from the psychrophilic and mildly halophilic bacteriumVibrio salmonicidaand from the mesophilic brackish water bacterium Vibrio choleraehave been cloned, over-expressed inEscherichia coli, and purified.