Abstract

The nucleocapsid (NP) protein of Newcastle disease virus (NDV) and its derivative (NP_cfus ) containing the myc region and six histidine residues fused to its C-terminus were expressed abundantly in Escherichia coli. The proteins were purified by sucrose gradient centrifugation. Both the NP and NP_cfus proteins self-assembled into ring-like particles with a diameter of 24 +- 2 nm around a central hole of 7 +- 1 nm. Some of these ring-like particles stacked together to form nucleocapsid-like structures which are heterogeneous in length with a diameter of 20 +- 2 nm and a central hollow of 5 +- 1 nm. Only a very small amount of the monomers in the particles was linked by inter-molecular disulfide bonds. Fusion of the C-terminal end to 29 amino acids inclusive of the myc epitope and His-tag did not impair ring assembly but inhibited the formation of the long herringbone structures. Immunogold labeling of the particles with the anti-myc antibody showed that the C-terminus of the NP_cfus protein is exposed on the surface of these ring-like particles.

• Keywords: protein assembly; fusion protein; NDV; nucleocapsid