The IFN-gamma response of the murine invariant chain gene is mediated by a complex enhancer that includes several MHC class II consensus elements.

IFN-gamma induces the expression of the MHC class II-associated invariant chain (IN) protein in a variety of cells of nonlymphoid origin. Here we analyze the transcription from the murine invariant chain gene and delimit the cis-acting sequences which confer IFN-gamma responsiveness in human fibroblasts. The major start of transcription of the gene is located 29 bp 3' of a TATA box and 85 bp 5' of the single ATG codon which opens the reading frame. To identify the regulatory elements of the murine IN promoter which respond to IFN-gamma, the 5' flanking region of the gene including its capsite and 85 bp of coding region have been cloned in front of the bacterial chloramphenicol acetyl transferase (CAT) gene. Examination of this construct and various 5' and 3' deletion mutants for IFN-gamma inducibility in transient transfection assays revealed that DNA sequences between -261 and -189 were essential and sufficient for the induction. Removal of sequences between -215 and -189 reduced inducibility of the IN-promoter and abolished the capacity of the element to transmit inducibility to a heterologous promoter. Single or multiple base changes in other parts of the element also abolished inducibility. Cotransfection of a 350 molar excess of the IFN-gamma response element with an inducible IN-CAT chimeric construct blocked inducibility, suggesting positive regulation. A protein binding to the central part of the IFN-gamma response element was detectable in gel retardation experiments; it was active only in extracts from IFN-gamma-treated cells.