Members of the Rel/NF-κB and IκB families of proteins. The arrows indicate the endoproteolytic cleavage sites of p105 and p100 which give rise to p50 and p52, respectively. Black boxes indicate the PEST domains, shaded boxes on Bcl-3 indicate transactivation domains, and gray boxes on RelB indicate leucine zipper domains. Abbreviations: RHD, Rel homology domain; ANK, ankyrin repeat; SS, signal-induced phosphorylation sites.