Toxic component of a type II toxin-antitoxin (TA) system. ChpB is a sequence-specific mRNA and (weak) tmRNA endoribonuclease that inhibits protein synthesis and induces bacterial stasis. Cleavage is independent of the ribosome. Cleavage occurs at ACY sequences where Y is not C. The endoribonuclease activity is not as strong as that of MazF. The endoribonuclease activity (a toxin) is inhibited by its labile cognate antitoxin ChpS. Toxicity results when the levels of ChpS decrease in the cell, leading to mRNA degradation. Both ChpS and ChpB probably bind to the promoter region of the chpS-chpB operon to autoregulate their synthesis. Stimulated in vitro in a concentration-dependent fashion by extracellular death factor (EDF, a quorum sensing pentapeptide sequence NNWNN, probably produced from the zwf gene product glucose-6-phosphate 1-dehydrogenase), which is able to overcome inhibition by cognate antitoxin ChpS. Homodimer, interacts with ChpS, which inhibits the endoribonuclease activity. Part of the chpS-chpB operon. No visible phenotype (PubMed:8083180, PubMed:12972253). Belongs to the PemK/MazF family.