This family consists of several Enterobacterial post-segregation antitoxin CcdA proteins. The F plasmid-carried bacterial toxin, the CcdB protein, is known to act on DNA gyrase in two different ways. CcdB poisons the gyrase-DNA complex, blocking the passage of polymerases and leading to double-strand breakage of the DNA. Alternatively, in cells that overexpress CcdB, the A subunit of DNA gyrase (GyrA) has been found as an inactive complex with CcdB. Both poisoning and inactivation can be prevented and reversed in the presence of the F plasmid-encoded antidote, the CcdA protein [1].

1: Interactions of CcdB with DNA gyrase. Inactivation of Gyra, poisoning of the gyrase-DNA complex, and the antidote action of CcdA. Bahassi EM, O'Dea MH, Allali N, Messens J, Gellert M, Couturier M; J Biol Chem 1999;274:10936-10944. PMID:10196173