HUMAN RELB (I-REL) FUNCTIONS AS A KAPPA-B SITE-DEPENDENT TRANSACTIVATING MEMBER OF THE FAMILY OF REL-RELATED PROTEINS

RelB belongs to the family of Rel-related proteins, dimers of which de termine NF-kappa B activity. The murine RelB protein has been reported to be a dimerizing partner in kappa B-binding complexes which are cap able of transactivation. On the other hand, the I-Rel protein, the pre sumed human homolog of RelB, was proposed to be an inhibitor whose pre sence in dimeric complexes interfered with their kappa B binding and t herefore interfered also with transactivation. We demonstrate that hum an RelB (I-Rel) forms with p50 and p52 (p50B) kappa B-binding heterodi meric complexes which potently transactivate kappa B-dependent constru cts in transfection studies. It is concluded that human RelB (I-Rel) a nd murine RelB can both function as transactivators and that no signif icant species-specific differences exist.