ROLE OF GTPASE ACTIVITY OF MURINE MX1 PROTEIN IN NUCLEAR-LOCALIZATION AND ANTIINFLUENZA VIRUS ACTIVITY

Murine Mx1 protein is an interferon-inducible GTPase which localizes in nuclei and inhibits influenza virus infection. Wild-type Mx1 and two mutant Mx1 proteins, each carrying a single mutation either in the GTP-binding motif (S50I) or in the self-assembly motif (C71S), were expressed in MDCK cells. Wild-type Mx1 localized in nuclei, forming small granules with minute dots, and inhibited influenza virus growth. Mutant S50I, which had no GTP-binding or GTPase activities, formed linear structures in nuclei and lacked anti-viral activity, while C71S appeared diffuse in nuclei as minute dots without granules, but retained the inhibitory activity against influenza virus growth. A correlation existed between GTPase activity, intranuclear distribution and antiviral activity. We concluded that GTPase activity is essential for expression of the biological activity of Mx1 protein.