Toxic component of a type II toxin-antitoxin (TA) system (PubMed:19423702, PubMed:24257752, PubMed:8645296). A ribosome-associated translation-dependent mRNA interferase. Inhibits translation by sequence-specific cleavage of mRNA. Prefers either in-frame or out-of-frame 5'-AAA-3' codons (lysine). Cleaves also the first three AAAs of stretches of four or more A sequences. 20% of codons containing AA are cleaved and occassionally cuts even at a single A (PubMed:19423702). Forms a complex with the antitoxin HigA which inhibits the mRNA interferase activity (PubMed:19423702). The heterodimer dimerizes to form a HigB-(HigA)2-HigB tetramer that is able to bind to the DNA (PubMed:24257752).