Tomato mosaic virus (ToMV; genus， Tobamovirus) is a member of the alpha-like virus superfamily of positive-strand RNA viruses， which includes many plant and animal viruses of agronomical and clinical importance. The genomes of alpha-like viruses encode replication-associated proteins that contain methyltransferase， helicase and/or polymerase domains. The three-dimensional structure of the helicase domain fragment of ToMV has been determined， but the structures of the other domains of alpha-like virus replication proteins are not available. In this study， we expressed full-length ToMV replication-associated protein 130 K， which contains the methyltransferase and helicase domains， using the baculovirus-silkworm expression system and purified the recombinant protein to near homogeneity. Purified 130 K， which was stable in phosphate buffer containing magnesium ions and ATP， formed a dimer in solution and hydrolyzed nucleoside 5'-triphosphates.