The NFKB complex consists of NFKB1 or NFKB2 bound to REL, RELA, or RELB. The NFKB complex is inhibited by I kappa B proteins (NFKBIA, or NFKBIB), which inactivate NF kappa B by trapping it in the cytoplasm. Phosphorylation of serine residues on the I kappa B proteins by kinases (IKBKA, or IKBKB,) marks them for destruction via the ubiquitination pathway, thereby allowing activation of the NF kappa B complex.