AbiEi_4 is the cognate antitoxin of the type IV toxin-antitoxin 'innate immunity' bacterial abortive infection (Abi) system that protects bacteria from the spread of a phage infection. The Abi system is activated upon infection with phage to abort the cell thus preventing the spread of phage through viral replication. There are some 20 or more Abis, and they are predominantly plasmid-encoded lactococcal systems. TA, toxin-antitoxin, systems on plasmids function by killing cells that lose the plasmid upon division. AbiE phage resistance systems function as novel Type IV TAs and are widespread in bacteria and archaea. The cognate antitoxin is Pfam:PF13338 [1].

1: A widespread bacteriophage abortive infection system functions through a Type IV\ttoxin-antitoxin mechanism. Dy RL, Przybilski R, Semeijn K, Salmond GP, Fineran PC; Nucleic Acids Res. 2014;42:4590-4605. PMID:24465005