Self-interaction of Citrus tristeza virus p33 protein via N-terminal helix

Citrus tristeza virus (CTV), the most economically important viral pathogen of citrus, encodes a unique protein, p33. CTV p33 shows no similarity with other known proteins, yet plays an important role in viral pathogenesis: it extends the virus host range and mediates virus ability to exclude superinfection by other variants of the virus. Previously we demonstrated that p33 is an integral membrane protein and appears to share characteristics of viral movement proteins. In this study, we show that the p33 protein self-interacts in vitro and in vivo using co-immunoprecipitation, yeast two hybrid, and bimolecular fluorescence complementation assays. Furthermore, a helix located at the N-terminus of the protein is required and sufficient for the protein self-interaction.