Toxic component of a type I toxin-antitoxin (TA) system. The sibD sRNA probably represses expression of ibsD mRNA, either by destabilizing the transcript and/or preventing its translation (Probable). Expression of the proteinaceous toxin is controlled by antisense sRNA SibD. None seen. An isbD overproducing strain cannot be made in the absence of the sibD gene. Part of the SIBd repeat region (formerly known as QUAD1d), encoded on the opposite strand from the sibD (formerly known as rygD) RNA. Belongs to the Ibs toxic protein family.