Toxic component of a toxin-immunity protein module, which functions as a cellular contact-dependent growth inhibition (CDI) system. CDI modules allow bacteria to communicate with and inhibit the growth of closely related neighboring bacteria in a contact-dependent fashion (PubMed:21829394, PubMed:25174572). The C-terminal 289 residues (the CT fragment) has a strong DNase activity in the presence of Zn(2+), completely degrading supercoiled and linear plasmids, and inhibits growth. In the presence of Mg(2+) it nicks dsDNA (PubMed:23236156). Toxic activity is neutralized by coexpression of the cognate immunity protein CdiI-o11-EC869, but not by non-cognate immunity proteins from other toxin-immunity modules or other strains of E.coli (PubMed:21829394). Gains access to the cytoplasm of target cells by using integral inner membrane protein YciB (PubMed:26305955). Expression of this locus confers protection against other bacteria carrying the locus. Bind 1 Zn(2+) per subunit. Interacts with cognate immunity protein CdiI-o11-EC869, which blocks its toxic DNase activity. Toxin translocation into the target cell depends on the proton motive force of the target cell, but not on tolA or tonB. A beta-hairpin (residues 322-332) fits into a pocket in cognate immunity protein CdiI-o11 and helps confer immunity protein specificity (PubMed:23236156, PubMed:26449640). The inner membrane translocation domain (IMTD) targets the toxin to a specific target cell inner membrane protein (YciB in this case), which delivers the toxin to the target cell cytoplasm. Exchanging this IMTD between CdiA proteins alters the inner membrane protein delivery system but not the CdiI immunity protein, strongly suggesting CdiI recognizes only the toxic domain (PubMed:26305955). The sequences characterized in (PubMed:21829394) and crystallized in (PubMed:23236156) are actually derived from cdiA-CTo11/cdiIo11, an orphan cdiA-CT/cdiI module that only encodes the cdiA CT fragment and its associated cdiI. It is however identical to that shown in this entry, which does have the elements necessary for gene expression.