title: Colicin E2 is DNA endonuclease.
abstract: Colicin E2 purified by conventional methods contains a tightly bound low-molecular-weight protein, as has been found with purified colicin E3 [Jakes,N.&Zinder,N.D.(1974) Proc. Natl. Acad. Sci. USA 71, 3380-3384]. Such E2 preparations do not cause DNA cleavage in vitro. After separation from the low-molecular-weight protein, colicin E2 retained the original in vivo killing activity, and in addition showed a high activity in vitro in cleaving various DNA molecules, such as a ColE1 hybrid plasmid and DNAs from Escherichia coli, lambda phage, chiX174 phage, and simian virus 40. The low-molecular-weight protein ("E2-immunity protein") specifically prevented this in vitro DNA cleavage reaction, i.e., had an "immunity function." The results demonstrate that colicin E2 itself is a DNA endonuclease and explain the in vivo effects caused by E2 in sensitive cells as well as the mechanism of immunity in E2-colicinogenic cells.
mesh_terms: D003087:Colicins / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D004247:DNA / Q000378:metabolism*; D004269:DNA, Bacterial / Q000378:metabolism; D004270:DNA, Circular / Q000378:metabolism; D004720:Endonucleases / Q000378:metabolism*; D006146:Guanidines; D008970:Molecular Weight
chemical_list: D003087:Colicins; D004269:DNA, Bacterial; D004270:DNA, Circular; D006146:Guanidines; D004247:DNA; D004720:Endonucleases