Molecular cloning of double-stranded RNA inducible Mx genes from Atlantic salmon (Salmo salar L.).

Mx proteins are induced by type I interferons in mice and humans and inhibit the replication of several negative-stranded RNA viruses. In this work Mx genes in Atlantic salmon were studied using the double stranded RNA, polyinosinic: polycytidylic acid (poly I:C), to induce interferon production. Northern blot analysis showed Mx mRNA in liver, head kidney and gills 2 days after poly I:C injection of fish, but not in untreated fish or fish injected with saline or LPS. Mx transcripts of 2.4 and 1.9 kb were detected in the liver. By screening of a cDNA library, three different full length Mx cDNA clones, ASMx1, ASMx2 and ASMx3, were identified and sequenced. The deduced ASMx proteins all contain 623 amino acids and show the tripartite GTP-binding motif typical of vertebrate Mx proteins. ASMx1 and ASMx2 may represent alleles of the same gene whereas ASMx3 represents a different gene. The deduced ASMx proteins showed 96 to 98% sequence identity with rainbow trout Mx1 and Mx3 and about 88% identity with rainbow trout Mx2 protein.