Whereas the majority of IκBs (IκBα, IκBβ, IκBε, p105 (also known as NF-κB1), p100 (also known as NF-κB2)) serve as inhibitors of NF-κB, IκBξ and Bcl-3 instead potentiate NF-κB transactivation in the nucleus. p100 and p105 are precursors of the p52 and p50 NF-κB subunits, respectively.