Homotypic interaction and multimerization of nucleocapsid protein of tomato spotted wilt tospovirus: identification and characterization of two interacting domains.

The nucleocapsid protein (N) of tomato spotted wilt tospovirus (TSWV) plays a central role in the viral life cycle. With the aid of the yeast two-hybrid system and surface plasmon resonance analysis, homotypic interaction and multimerization of the N protein was detected. Analysis of deletion mutants identified two binding regions in the protein, located at the N terminus (amino acids 1-39) and the C terminus (amino acids 233-248), respectively, implying a "head-to-tail" interaction of the N terminus with the C terminus to form a multimeric chain. Further characterization of the binding domains was performed by site-directed mutagenesis. Two phenylalanines (F242 and F246) highly conserved in the N proteins within the Tospovirus genus were shown to play a crucial role in the interaction.