Toxic component of a type III toxin-antitoxin (TA) system. An endoribonuclease that is probably sequence-specific. It is neutralized by its cognate antitoxin RNA AntiQ, which has 2.8 35 nucleotide-long repeats. Cannot be cloned in L.lactis subsp. cremoris strain NZ9000 in the absence of the antitoxin gene; expression in strain NZ9000 even in the presence of antiQ inhibits growth in a bacteriostatic fashion (PubMed:23279123). Confers resistance to 936 and c2 phages but not P335 phages in L.lactis, causes an abortive infection (Abi phenotype). Viral DNA is replicated but not cleaved from its concatemeric form, while the viral major structural protein is produced normally in the presence of this protein (PubMed:9835558). Operon expression in E.coli confers resistance to 3 phages of the Myoviridae family (T4, RB69 and phage 2) and 1 of the Siphoviridae family (T5), but not other tested phages (T1, T3, lambda vir, HK97, Mu and pilH alpha). The presence of this operon in L.lactis subsp. lactis strain IL1403 during phage P008 infection alters the viral transcription profiles (PubMed:23813728). Forms a triangular heterohexamer with a single 35-nt-long repeat of RNA antitoxin AntiQ. Constitutively expressed in the presence or absence of phage P0008 (in L.lactis subsp. lactis strain IL1403) (at protein level); in the presence of phage the abiQ transcript level decreases while the antiQ transcript does not. Part of the antiQ-abiQ operon. Loss of resistance to bacteriophage. Belongs to the ToxN/AbiQ toxin family. It is uncertain whether Met-1 or Met-12 is the initiator.