The Dynamin family of microtubule-associated proteins function as GTPases that are involved in microtubule bundling and endocytosis. In mice, Mx1 (myxovirus resistance protein 1) is member of the Dynamin family that is involved in the immune response to viral infections. Localized to the cytoplasm, Mx1 is localized to the nucleus where, upon induction by IFN-alpha/IFN-beta, it provides selective resistance to infection by the highly lethal H5N1 influenza virus. In humans, MxA and MxB function in a similar manner to Mx1 and Mx2, conferring resistance to specific target viruses. Mx3 is a rat-specific member of the myxovirus resistance protein family.