The invention provides for isolated nucleic acids encoding an Mda-5 polypeptide as shown in SEQ ID NO:1. The invention also provides for isolated nucleic acids comprising derivatives of the sequence of SEQ ID NO:1 that encode polypeptides functionally equivalent to Mda-5. The invention further provides for fragments of the isolated nucleic acid of SEQ ID NO:1 that encode polypeptides having Mda-5 biological activity. Vectors comprising these isolated nucleic acids and host cells comprising these vectors are also provided by the instant invention.