Replacement of 198MQMDII203 of mouse IRF-1 by 197IPVEVV202 of human IRF-1 abrogates induction of IFN-beta, iNOS, and COX-2 gene expression by IRF-1.

Interferon regulatory factor-1 (IRF-1) is a transcription factor exhibiting functional diversity because of its ability to activate transcription from promoters of several IRF-1-dependent genes. It is a modular protein, where the overall structure is not essential for function of its individual domains. A comparison of the mouse and human IRF-1 amino acid sequences enabled us to identify a stretch of six amino acids (198-203) within the transactivation domain of mouse IRF-1, 198MQMDII(203) to be different from that of the human IRF-1, 197IPVEVV(202). This indicated a possible functional significance of the six amino acid stretches in the two IRF-1 molecules. The murine IRF-1 sequence at 198-203 (MQMDII) was replaced by IPVEVV. Recombinant wild type mouse IRF-1 with 198MQMDII(203) and its mutant form with 198IPVEVV(203), expressed as GST-IRF-1-fusion proteins, showed similar DNA-binding activity. However, ectopic expression of the wild type and mutant IRF-1 in the human embryonic kidney (HEK-293) cells showed the effect of replacement of this region on expression of a few chromosomal genes that are transcriptionally activated by IRF-1 viz. IFN-beta, iNOS, and COX-2 genes. In our study, expression of wild type IRF-1 activated these genes as judged by RT-PCR but the mutant IRF-1 did not show this effect. Thus, the MQMDII (198-203 a.a.) region of mouse IRF-1 has a functional context in relation to expression of IRF-1-inducible genes.