Toxic component of a type I toxin-antitoxin (TA) system. Overexpression causes cessation of growth. The sibE sRNA probably represses expression of ibsE mRNA, either by destabilizing the transcript and/or preventing its translation. Expression of the proteinaceous toxin is controlled by antisense sRNA SibE. None seen. An isbE overproducing strain cannot be made in the absence of the sibE gene. Part of the SIBe repeat region, encoded on the opposite strand from the sibE RNA. Belongs to the Ibs toxic protein family.