Toxic component of a type I toxin-antitoxin (TA) system. Overexpression causes cessation of growth and rapid membrane depolarization. Overexpression induces stress-response, the psp phage shock and a number of membrane protein genes. The sibC sRNA prevents the toxic effects of IbsC overproduction, either by destabilizing the transcript and/or preventing its translation. Expression of the proteinaceous toxin is controlled by antisense sRNA SibC. None seen. An isbC overproducing strain cannot be made in the absence of the sibC gene. Part of the SIBc repeat region (formerly known as QUAD1c), encoded on the opposite strand from the sibC (formerly known as rygC) RNA. Belongs to the Ibs toxic protein family.