DIFFERENTIAL REGULATION OF NF-KAPPA-B2(P100) PROCESSING AND CONTROL BY AMINO-TERMINAL SEQUENCES

Proteolytic degradation of the C-terminal region of NF-kappa B precurs ors to their active DNA binding forms represents an important regulato ry step in the activation of NF-kappa B. NF-kappa B2(p100) is found ub iquitously in the cytoplasm; however, the site and mechanism of proces sing to p52 have not previously been defined. We show by deletion mapp ing that processing of NF-kappa B2(p100) terminates at alanine 405 to generate p52 and is prevented by specific inhibitors of the multicatal ytic proteinase complex, Although the C-terminal I kappa B-like domain of NF-kappa B2(p100) was constitutively phosphorylated, disruption of this phosphorylation by mutagenesis demonstrated that it was not requ ired as a signal to mediate processing. Mutational analysis further sh owed that cleavage of NF-kappa B2 is not dependent on a specific seque nce motif adjacent to alanine 405, the ankyrin repeats, or other C-ter minal sequences but is directed by structural determinants amino termi nal to the cleavage site, within the Rel homology domain and/or the gl ycine hinge region. The level of processing of NF-kappa B2(p100) was m uch lower than that of NF-kappa B1(p105) and differed from that of I k appa B-alpha, suggesting differential control of processing of NF-kapp a B/I kappa B family members.