Interferon-inducible Mx proteins in fish

Mr proteins are members of a family of interferon-inducible genes expressed when cells are treated with double-stranded RNA or virus infection. These proteins are important components of the antiviral response and form the fi rst line of the body's defense against virus infections. The exact mechanis m of action for these proteins has not been discovered, but mice missing th e Mx genes are extremely sensitive to influenza virus infection. Mammals ha ve between two and three Mx genes whose functions may vary with regard to t he inhibition of a specific virus, cellular localization, and activity The cDNA of three rainbow trout Mr proteins has been cloned and a comparison of their sequences with that of avian and mammalian species reveals striking conservation of domains. They all maintain the tripartite ATP/GTP binding d omain and the dynamin family signature in the amino terminal half of the pr otein. In the carboxyl terminal half of the Mr proteins are the localizatio n signals and the leucine zipper motifs which account for the trimerization of Mr in the cell. Like the rat and human Mr proteins, the different trout Mr proteins exhibit distinctly different immunohistochemical staining patt erns in cells transfected with plasmids expressing RBTMx1, RBTMx2, or RBTMx 3. To date, the antiviral function of the trout Mx proteins has not been sa tisfactorily established.