Bcl-3 Background Information On the basis of both functional and structural considerations, members of the IkB family of proteins can be divided into three groups. The first of these groups, IkB-a, includes the avian protein pp40 and the mammalian MAD-3, both of which inhibit binding of p50-p65 NFkB complex or Rel protein to their cognate binding sites but do not inhibit the binding of p50 homodimer to kB sites, suggesting that the IkB-a family binds to the p65 subunit of p50-p65 heterocomplex through ankyrin repeats. The second member of the IkB family is represented by a protein designated IkB-b. The third group of IkB proteins is represented by IkB-g, a protein identical in sequence with the C-terminal domain of the p110 precursor of NFkB p50 and expressed predominantly in lymphoid cells. The proto-oncogene Bcl-3, believed to be involved in certain human B cell leukemias, encodes a protein that functions as an IkB-like molecule for native NFkB but is specific for the p50 subunit.
