This entry defines several short bacterial proteins, typically about 75 amino acids long, which are always found as part of a pair (at least) of small genes. The other protein in the pair always belongs to a family of plasmid stabilisation proteins (IPR007712). It is likely that this protein and its partner comprise some form of addiction module - a pair of genes consisting of a stable toxin and an unstable antitoxin which mediate programmed cell death - although these gene-pairs are usually found on the bacterial main chromosome.