tokens: Although serine phosphorylation has been shown to induce ubiquitination and subsequent proteasome-mediated degradation of I kappa B-alpha , little is known about the mechanisms that lead to release of active NF-kappa B in T cells as a consequence of tyrosine phosphorylation of I kappa B-alpha [ Imbert , V. , Rupec , R.A. , Livolsi , A. , Pahl , H.L. , Traenckner , B.M. , Mueller-Dieckmann , C. , Farahifar , D. , Rossi , B. , Auberger , P. , Baeuerle , P. & Peyron , J.F. ( 1996 ) Cell 86 , 787 -- 798 ] .