Non-covalent interaction between nucleocapsid protein of Tula hantavirus and small ubiquitin-related modifier-1, SUMO-1

To find cellular binding counterparts for the nucleocapsid protein (N) of Tula hantavirus (TULV), two cDNA libraries were screened using yeast two-hybrid systems based on LexA and Gal4 transcription factors. Five cDNA clones encoding SUMO-1 (Small Ubiquitin-related MOdifier, also known as sentrin) were selected in the LexA system. Confocal microscopy revealed that, in infected cells, TULV N protein and SUMO-1 colocalize at the perinuclear area providing further evidence for interaction between the two proteins. Neither endogenous nor transiently expressed SUMO-1 was found to be covalently linked to the N protein. Additional evidence that the interaction is non-covalent was obtained in immunoprecipitation experiments: N protein-specific antibodies precipitated SUMO-1 from TULV-infected Vero E6 cell lysate. By using a pepscan assay, two basic amino acid stretches in the N-terminal part of SUMO-1 were shown to be involved in the interaction.