ASSEMBLY OF RECOMBINANT NEWCASTLE-DISEASE VIRUS NUCLEOCAPSID PROTEIN INTO NUCLEOCAPSID-LIKE STRUCTURES IS INHIBITED BY THE PHOSPHOPROTEIN

A recombinant baculovirus expressing the nucleocapsid gene (NP) of New castle disease virus (NDV), a member of the genus Rubulavirus, has bee n generated and shown to express the native protein to high levels in insect cells. In contrast to the NP protein of the rubulavirus human p arainfluenza virus 2, the NDV protein has been demonstrated by electro n microscopy and caesium chloride gradient analysis to be capable of s elf-assembly in vivo to form nucleocapsid-like structures in the absen ce of other NDV proteins. These structures, which contained RNA that w as resistant to micrococcal nuclease digestion, were also observed whe n the protein was expressed in E. coli, a phenomenon which was not inh ibited by the presence of a 40 amino acid fusion region at the amino t erminus of the protein, Further, the formation of these structures was inhibited by the co-expression of the phosphoprotein (P). Therefore, we conclude that the P protein acts as a chaperone, preventing uncontr olled encapsidation of non-viral RNA by NP protein.