Characterization of a novel serine/threonine kinase associated with nuclear bodies

A novel protein kinase, Mx-interacting protein kinase (PKM), has been ident ified in a yeast two-hybrid screen for interaction partners of human MxA, a n interferon-induced GTPase with antiviral activity against several RNA vir uses. A highly conserved protein kinase domain is present in the N-terminal moiety of PKM, whereas an Mx interaction domain overlaps with C-terminal P EST sequences. PKM has a molecular weight of about 127,000 and exhibits hig h sequence homology to members of a recently described family of homeodomai n-interacting protein kinases, Recombinant PKM has serine/threonine kinase activity that is abolished by a single amino acid substitution in the ATP b inding domain (K221W). PKM catalyzes autophosphorylation and phosphorylatio n of various cellular and viral proteins. PKM is expressed constitutively a nd colocalizes with the interferon-inducible Sp100 protein and murine Mx1 i n discrete nuclear structures known as nuclear bodies.