We have previously defined the lipopolysaccharide (LPS)-responsive element (LRE) in the promoters of murine RANTES (regulated on activation normal T-cell expressed) (MuRantes) and murine IP-10/crg-2, chemokines which have potent chemotactic properties for inflammatory cells including monocytes and T lymphocytes. In the present work, we studied the transcriptional mechanism of MuRantes gene induction by virus and compared it with that of LPS in an effort to understand the host responses to virus and bacterial toxins at the molecular level. MuRantes mRNA expression is induced by Newcastle disease virus (NDV) and LPS in the RAW 264.7 macrophage cell line and peritoneal macrophages of LPS-responsive C3HeB/FeJ mice. In LPS-hyporesponsive C3H/HeJ mice, only NDV induces this chemokine gene, indicating that the pathways of transcriptional activation by NDV and LPS are not identical. Using a transient transfection assay, the minimal virus-responsive element (VRE) was localized between nt -175 and -116. The VRE contains previously defined LRE motif 1 (TCAYRCTT) and motif 3 ((T/A)GRTTTCA(G/C)TTT), which were shown to also be important for initiation of transcription by virus. NDV-stimulated nuclear extracts were tested for trans-activating factors able to bind the VRE. The chromosomal protein HMG-I(C) was shown to bind the 3'-A.T-rich domains of the VRE, and the presence of HMG-I(C) was demonstrated in the VRE-protein complex formed with nuclear extracts from NDV-stimulated, but not unstimulated cells. These findings demonstrate the role of HMG-I(C) in activation of MuRantes promoter by NDV.