MEASLES-VIRUS NUCLEOCAPSID PROTEIN EXPRESSED IN INSECT CELLS ASSEMBLES INTO NUCLEOCAPSID-LIKE STRUCTURES

The gene encoding the major nucleocapsid, N, protein of measles virus has been inserted into a baculovirus vector under the control of the p olyhedrin promoter. Insect cells infected with this recombinant baculo virus synthesize high levels of measles N protein, up to 40 % of total soluble cell protein. The recombinant protein is recognized by sera f rom convalescent patients, vaccinees and patients with subacute sclero sing panencephalitis and thus could form the basis of a simple diagnos tic assay. Nucleocapsid-like structures, similar to those found in mam malian cells infected with measles virus. can be observed in both the nucleus and cytoplasm of the infected insect cells. These have many st ructural features in common with nucleocapsids found in measles virus- infected cells, but are longer (up to 2 mum) and have a lower buoyant density. Measles N protein thus appears to be capable of assembling in to nucleocapsid-like structures in the absence of measles virion RNA o r other viral proteins.