Accumulated NF-kB-inducing kinase (NIK) activates I kappa-B kinase alpha (IKKA) by directly phosphorylating the Ser176 and Ser180 with in the activation loop of IKKA. This phoshorylation is required for IKKA activity (Ling et al. 1998). Besides activating IKKA, NIK also serves as a docking molecule recruiting IKKA to p100 (Xiao et al. 2004).