Expression of the nucleoprotein of rabies virus in Escherichia coli and mapping of antigenic sites.

Investigations were performed to delineate the antigenic sites I and IV of rabies virus nucleoprotein (N), the former of which is well conserved among the rabies and rabies-related viruses. The N cDNA of the RC-HL strain was inserted into an expression vector pET3a, with which the E. coli BL21(DE3) was transformed. Upon induction with isopropyl-1-thio-beta-D-galactoside, the transformants produced a protein with a size (56 k-Da) almost identical to that of the authentic N protein. The protein also reacted with a panel of our N protein-specific monoclonal antibodies (N-MAbs) including the antibodies against the antigenic sites I and IV. By using the cDNA, various deletion mutants were generated and expressed in E. coli to examine the reactivity of mutant proteins with N-MAbs by Western blot analysis. Deletion of the C-terminal 67 amino acid residues did not abolish their reactivity with any of the N-MAbs specific for the sites I and IV. When 91 residues or more were deleted from the C-terminus, however, the protein lost the reactivity, indicating that the antigenic sites I and IV are mapped to a small region which is comprised of at most 24 amino acid residues from positions 360 to 383. Comparison of the 24-amino acid sequence with the corresponding region of N protein of several other Lyssavirus strains suggests that the antigenic site I is mapped to positions 360 to 369.