Colicin E8, a DNase which indicates an evolutionary relationship between colicins E2 and E3.

Colicin E8-J and its immunity protein were characterized with regard to their activities and gene structures. Colicin E8 is a complex of proteins A and B; protein A (the naked E8) exhibits an apparently nonspecific DNase activity that is inhibited by protein B (the immunity protein), as in the case of colicin E2. The nucleotide sequence of the downstream half of the colicin operon of ColE8-J was determined to be highly homologous to that of ColE2-P9, with the exception of the hot spot region of the 3'-terminal segment of the colicin gene and the adjacent immunity gene. The immE2-like gene of ColE3-CA38 was, as assumed previously, extensively homologous to the immE8 gene of ColE8-J, and thus, ColE8-J was shown to be situated between ColE2-P9 and ColE3-CA38 in the evolution of the E-group Col plasmids.