To understand the mechanisms involved in dsRNA-induced gene expression, we analyzed the poly(I/C)-induced transcription of the IFN-inducible chemokine gene IP-10 using the GRE cell line in which type I IFN genes have been deleted. Accumulation of IP-10 mRNA in GRE cells was more strongly stimulated by treatment with dsRNA than by IFN-alpha or IFN-gamma and was independent of protein synthesis. This same pattern of response was produced when GRE cells were transiently transfected with a plasmid containing 243 bases of sequence from the promoter of the murine IP-10 gene linked to the chloramphenicol acetyltransferase reporter gene. Deletion- and site-specific mutagenesis of the 243 base pair fragment indicated that an ISRE located between residues -204 and -228 was a primary target site for the action of dsRNA on this promoter. This was confirmed by results showing that two copies of this ISRE tandemly arrayed in front of the thymidine kinase promoter were able to mediate reporter gene transcription in dsRNA-stimulated cells. At least one of the two NF kappa B binding sites present in the 243 base pair IP-10 promoter is also necessary for response to dsRNA; mutation of both sites eliminates promoter activity. Thus the ISRE and one NF kappa B site cooperate to produce transcriptional response to dsRNA.