In vivo formation of IRF-1 homodimers

Interferon regulatory factor 1 (IRF-1) is a transcriptional activator which exerts different biological activities. IRF-1 activates interferon induced genes as well as genes which are not directly Linked to the interferon sys tem, such as the ICE protease gene. IRF-1 activity is post-transcriptionall y regulated in addition to transcriptional regulation by interferons, cytok ines, hormones and many other factors. This includes heterodimerisation wit h activators and repressors of transcription. These protein interactions mo dulate the transactivating capacity of IRF-1. By using a two-hybrid system, we demonstrate that IRF-1 forms homodimers in vivo. The homodimerization d omain was determined to be located in the N-terminal part of IRF-1 which be longs to the DNA-binding domain. Since this sequence is highly conserved be tween members of the IRF-family, our observation raises the question of hom odimerization of other IRFs through this domain. (C) Societe francaise de b iochimie et biologie moleculaire/Elsevier, Paris.