Genomic DNA containing the first four exons and upstream sequences of the interferon (IFN)-inducible chicken Mx gene was cloned and sequenced. The exon/intron structure of the chicken Mx gene resembles that of the mouse Mx1 gene: exon 1 is very small, the first intron contains a noncoding exon 1′ that is alternatively spliced in different chicken breeds and exon 2 harbors the ATG initiation codon. Exons 3 and 4 of the chicken and mouse Mx genes have identical lengths and the encoded polypeptides show a high degree of homology. Sequences upstream of the transcription start site functioned as an IFN-inducible promoter in chick and monkey cells when cloned in front of a promoterless luciferase reporter gene. Deletion analysis suggested that the sequence 5′AGTTTCGTTTCT3′ is of critical importance for inducibility. It conforms to the consensus sequence of the IFN stimulated response element (ISRE) present in Mx and other IFN-α/β-inducible promoters of mammals These results suggest that the ISRE motif has been conserved and that it regulates expression of IFN-inducible genes in both mammals and birds