Antitoxin component of a type II toxin-antitoxin (TA) system. May be involved in the regulation of cell growth. It acts as a suppressor of the endoribonuclease (inhibitory function) of ChpB protein. Both ChpS and ChpB probably bind to the promoter region of the chpS-chpB operon to autoregulate their synthesis. Interacts with ChpB, inhibiting its endoribonuclease activity. Part of the chpS-chpB operon. No visible phenotype. Belongs to the PemI family. Extended N-terminus. Extended N-terminus.