The invention provides for an isolated nucleic acid encoding Mda-5 (melanoma differentiation associated gene-5) and an isolated Mda-5 polypeptide. The invention further provides a vector comprising the nucleic acid encoding Mda-5, as well as a host cell comprising the vector. The invention provides an antibody which specifically binds to an Mda-5 polypeptide. The invention further provides a method for determining whether a compound is an inducer of Mda-5 gene expression and assays to determine whether a compound modifies the enzymatic activity of the Mda-5 polypeptide.