After being recruited into the NIK (NFkB-inducing kinase) complex, activated IKKA (I kappaB kinase alpha) phosphorylates serine residues 99, 108, 115, 123, 866, 870 and 872 located in both N- and C-terminal regions of NFKB2/p100. The phosphorylation of these specific serines is the prerequisite for ubiquitination and subsequent processing of p100. The C-terminal serine residues create a binding site for beta-TRCP (beta-transducinrepeat-containing protein), a ubiquitin E3 ligase (Xiao et al. 2001 & 2004, Liang et al. 2006).