The present invention relates to polypeptides that inhibit the NF-.kappa.B signaling pathway and polynucleotides encoding the same. The present invention further provides methods for the modulation of and/or treatment of inflammatory responses, oncogenesis, viral infection; the regulation of cell proliferation and apoptosis; and regulation of B or T lymphocytes in antigenic stimulation, by administering the polypeptides of the present invention to a subject in need thereof. Finally, the present invention provides a method of identifying polypeptides that modulate oligomerization of NEMO.