2 FACTORS, IRF1 AND KBF1 NF-KAPPA-B, COOPERATE DURING INDUCTION OF MHC CLASS-I GENE-EXPRESSION BY INTERFERON-ALPHA-BETA OR NEWCASTLE-DISEASE VIRUS/

The expression of class I genes of the Major Histocompatibility Comple x is stimulated by IFN. The promoter of these genes contains an interf eron response sequence (IRS) which overlaps the major enhancer. These elements are recognized by several protein factors, including IRF-1, w hich binds the IRS, and KBF1/NF-kappaB, which binds the enhancer. We d emonstrate here that infection by Newcastle Disease Virus (NDV) result s in an increased expression of class I genes, by a mechanism partiall y different from that of IFN, but that in both cases the cooperative a ction of IRF1 and KBF1/NF-kappaB is required. In F9 embryonal carcinom a cells, where KBF1/NK-kappaB activity cannot be detected, both types of stimuli are ineffective.