Tm-1, the protein product of Tm-1, a semidominant resistance gene of tomato, inhibits tomato mosaic virus (ToMV) replication by binding to ToMV replication proteins. Previous studies suggested the importance of the Tm-1 N-terminal region for its inhibitory activity; however, it has not been determined if the N-terminal region is sufficient for inhibition. Furthermore, the three-dimensional structure of Tm-1 has not been determined. In this study, an N-terminal fragment of Tm-1 (residues 1-431) as a fusion protein containing an upstream maltose-binding protein was expressed in E. coli Rosetta (DE3) cells at 30 degrees C and then purified. The solubility of the fusion protein was greater when the cells were cultured at 30 degrees C than when cultured at lower or higher temperatures. The purified N-terminal Tm-1 fragment from which the maltose-binding protein tag had been removed has inhibitory activity against ToMV RNA replication. Crown Copyright (C) 2013 Published by Elsevier Inc. All rights reserved.