Toxic component of a type I toxin-antitoxin (TA) system (Probable). When overexpressed kills cells within 2 minutes; causes collapse of the transmembrane potential and arrest of respiration (PubMed:3019679). Probably inactive in strain K12 MG1655 due to a genetic locus rearrangement, the locus for its antisense antitoxin RNA is missing. Belongs to the Hok/Gef family.